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eval.txt      For Vim version 8.2.  Last change: 2022 May 13


                  VIM REFERENCE MANUAL    by Bram Moolenaar


Expression evaluation                   expression expr E15 eval
                                                        E1002
Using expressions is introduced in chapter 41 of the user manual usr_41.txt.

Note: Expression evaluation can be disabled at compile time.  If this has been
done, the features in this document are not available.  See +eval and
no-eval-feature.

This file is mainly about the backwards compatible (legacy) Vim script.  For
specifics of Vim9 script, which can execute much faster, supports type
checking and much more, see vim9.txt.  Where the syntax or semantics differ
a remark is given.

1.  Variables                   variables
    1.1 Variable types
    1.2 Function references             Funcref
    1.3 Lists                           Lists
    1.4 Dictionaries                    Dictionaries
    1.5 Blobs                           Blobs
    1.6 More about variables            more-variables
2.  Expression syntax           expression-syntax
3.  Internal variable           internal-variables
4.  Builtin Functions           functions
5.  Defining functions          user-functions
6.  Curly braces names          curly-braces-names
7.  Commands                    expression-commands
8.  Exception handling          exception-handling
9.  Examples                    eval-examples
10. Vim script version          vimscript-version
11. No +eval feature            no-eval-feature
12. The sandbox                 eval-sandbox
13. Textlock                    textlock

Testing support is documented in testing.txt.
Profiling is documented at profiling.

==============================================================================
1. Variables                                            variables

1.1 Variable types 
                                        E712 E896 E897 E899 E1098
                                        E1107 E1135 E1138
There are ten types of variables:

                                                        Number Integer
Number          A 32 or 64 bit signed number.  expr-number
                The number of bits is available in v:numbersize.
                Examples:  -123  0x10  0177  0o177 0b1011

Float           A floating point number. floating-point-format Float
                {only when compiled with the |+float| feature} E1076
                Examples: 123.456  1.15e-6  -1.1e3

String          A NUL terminated string of 8-bit unsigned characters (bytes).
                expr-string Examples: "ab\txx\"--"  'x-z''a,c'

List            An ordered sequence of items, see List for details.
                Example: [1, 2, ['a', 'b']]

Dictionary      An associative, unordered array: Each entry has a key and a
                value. Dictionary
                Examples:
                        {'blue': "#0000ff", 'red': "#ff0000"}
                        #{blue: "#0000ff", red: "#ff0000"}

Funcref         A reference to a function Funcref.
                Example: function("strlen")
                It can be bound to a dictionary and arguments, it then works
                like a Partial.
                Example: function("Callback", [arg], myDict)

Special         v:false, v:true, v:none and v:null.  Special

Job             Used for a job, see job_start(). Job Jobs

Channel         Used for a channel, see ch_open(). Channel Channels

Blob            Binary Large Object. Stores any sequence of bytes.  See Blob
                for details
                Example: 0zFF00ED015DAF
                0z is an empty Blob.

The Number and String types are converted automatically, depending on how they
are used.

Conversion from a Number to a String is by making the ASCII representation of
the Number.  Examples:
        Number 123      -->     String "123" 
        Number 0        -->     String "0" 
        Number -1       -->     String "-1" 
                                                        octal
Conversion from a String to a Number only happens in legacy Vim script, not in
Vim9 script.  It is done by converting the first digits to a number.
Hexadecimal "0xf9", Octal "017" or "0o17", and Binary "0b10"
numbers are recognized
NOTE: when using Vim9 script or scriptversion-4 octal with a leading "0"
is not recognized.  The 0o notation requires patch 8.2.0886.
If the String doesn't start with digits, the result is zero.
Examples:
        String "456"    -->     Number 456 
        String "6bar"   -->     Number 6 
        String "foo"    -->     Number 0 
        String "0xf1"   -->     Number 241 
        String "0100"   -->     Number 64 
        String "0o100"  -->     Number 64 
        String "0b101"  -->     Number 5 
        String "-8"     -->     Number -8 
        String "+8"     -->     Number 0 

To force conversion from String to Number, add zero to it: 
        :echo "0100" + 0
       64 

To avoid a leading zero to cause octal conversion, or for using a different
base, use str2nr().

                                                TRUE FALSE Boolean
For boolean operators Numbers are used.  Zero is FALSE, non-zero is TRUE.
You can also use v:false and v:true, in Vim9 script false and true.
When TRUE is returned from a function it is the Number one, FALSE is the
number zero.

Note that in the command: 
        :if "foo"
        :" NOT executed
"foo" is converted to 0, which means FALSE.  If the string starts with a
non-zero number it means TRUE: 
        :if "8foo"
        :" executed
To test for a non-empty string, use empty(): 
        :if !empty("foo")

                                               falsy truthy
An expression can be used as a condition, ignoring the type and only using
whether the value is "sort of true" or "sort of false".  Falsy is:
        the number zero
        empty string, blob, list or dictionary
Other values are truthy.  Examples:
        0       falsy
        1       truthy
        -1      truthy
        0.0     falsy
        0.1     truthy
        ''      falsy
        'x'     truthy
        []      falsy
        [0]     truthy
        {}      falsy
        #{x: 1} truthy
        0z      falsy
        0z00    truthy

                                                        non-zero-arg
Function arguments often behave slightly different from TRUE: If the
argument is present and it evaluates to a non-zero Number, v:true or a
non-empty String, then the value is considered to be TRUE.
Note that " " and "0" are also non-empty strings, thus considered to be TRUE.
A List, Dictionary or Float is not a Number or String, thus evaluate to FALSE.

                E611 E745 E728 E703 E729 E730 E731 E908 E910
                E913 E974 E975 E976
List, Dictionary, Funcref, Job, Channel and Blob types are not
automatically converted.

                                                        E805 E806 E808
When mixing Number and Float the Number is converted to Float.  Otherwise
there is no automatic conversion of Float.  You can use str2float() for String
to Float, printf() for Float to String and float2nr() for Float to Number.

                        E362 E891 E892 E893 E894 E907 E911 E914
When expecting a Float a Number can also be used, but nothing else.

                                                no-type-checking
You will not get an error if you try to change the type of a variable.


1.2 Function references 
                                Funcref E695 E718 E1192
A Funcref variable is obtained with the function() function, the funcref()
function or created with the lambda expression expr-lambda.  It can be used
in an expression in the place of a function name, before the parenthesis
around the arguments, to invoke the function it refers to.  Example: 

        :let Fn = function("MyFunc")
        :echo Fn()
                                                       E704 E705 E707
A Funcref variable must start with a capital, "s:", "w:", "t:" or "b:".  You
can use "g:" but the following name must still start with a capital.  You
cannot have both a Funcref variable and a function with the same name.

A special case is defining a function and directly assigning its Funcref to a
Dictionary entry.  Example: 
        :function dict.init() dict
        :   let self.val = 0
        :endfunction

The key of the Dictionary can start with a lower case letter.  The actual
function name is not used here.  Also see numbered-function.

A Funcref can also be used with the :call command: 
        :call Fn()
        :call dict.init()

The name of the referenced function can be obtained with string(). 
        :let func = string(Fn)

You can use call() to invoke a Funcref and use a list variable for the
arguments: 
        :let r = call(Fn, mylist)

                                                                Partial
A Funcref optionally binds a Dictionary and/or arguments.  This is also called
a Partial.  This is created by passing the Dictionary and/or arguments to
function() or funcref().  When calling the function the Dictionary and/or
arguments will be passed to the function.  Example: 

        let Cb = function('Callback', ['foo'], myDict)
        call Cb('bar')

This will invoke the function as if using: 
        call myDict.Callback('foo', 'bar')

This is very useful when passing a function around, e.g. in the arguments of
ch_open().

Note that binding a function to a Dictionary also happens when the function is
a member of the Dictionary: 

        let myDict.myFunction = MyFunction
        call myDict.myFunction()

Here MyFunction() will get myDict passed as "self".  This happens when the
"myFunction" member is accessed.  When making assigning "myFunction" to
otherDict and calling it, it will be bound to otherDict: 

        let otherDict.myFunction = myDict.myFunction
        call otherDict.myFunction()

Now "self" will be "otherDict".  But when the dictionary was bound explicitly
this won't happen: 

        let myDict.myFunction = function(MyFunction, myDict)
        let otherDict.myFunction = myDict.myFunction
        call otherDict.myFunction()

Here "self" will be "myDict", because it was bound explicitly.


1.3 Lists 
                                                list List Lists E686
A List is an ordered sequence of items.  An item can be of any type.  Items
can be accessed by their index number.  Items can be added and removed at any
position in the sequence.


List creation 
                                                        E696 E697
A List is created with a comma-separated list of items in square brackets.
Examples: 
        :let mylist = [1, two, 3, "four"]
        :let emptylist = []

An item can be any expression.  Using a List for an item creates a
List of Lists: 
        :let nestlist = [[11, 12], [21, 22], [31, 32]]

An extra comma after the last item is ignored.


List index 
                                                        list-index E684
An item in the List can be accessed by putting the index in square brackets
after the List.  Indexes are zero-based, thus the first item has index zero. 
        :let item = mylist[0]           " get the first item: 1
        :let item = mylist[2]           " get the third item: 3

When the resulting item is a list this can be repeated: 
        :let item = nestlist[0][1]      " get the first list, second item: 12

A negative index is counted from the end.  Index -1 refers to the last item in
the List, -2 to the last but one item, etc. 
        :let last = mylist[-1]          " get the last item: "four"

To avoid an error for an invalid index use the get() function.  When an item
is not available it returns zero or the default value you specify: 
        :echo get(mylist, idx)
        :echo get(mylist, idx, "NONE")


List concatenation 
                                                        list-concatenation
Two lists can be concatenated with the "+" operator: 
        :let longlist = mylist + [5, 6]
        :let mylist += [7, 8]

To prepend or append an item, turn the item into a list by putting [] around
it.  To change a list in-place, refer to list-modification below.


Sublist 
                                                        sublist
A part of the List can be obtained by specifying the first and last index,
separated by a colon in square brackets: 
        :let shortlist = mylist[2:-1]   " get List [3, "four"]

Omitting the first index is similar to zero.  Omitting the last index is
similar to -1. 
        :let endlist = mylist[2:]       " from item 2 to the end: [3, "four"]
        :let shortlist = mylist[2:2]    " List with one item: [3]
        :let otherlist = mylist[:]      " make a copy of the List

Notice that the last index is inclusive.  If you prefer using an exclusive
index use the slice() method.

If the first index is beyond the last item of the List or the second item is
before the first item, the result is an empty list.  There is no error
message.

If the second index is equal to or greater than the length of the list the
length minus one is used: 
        :let mylist = [0, 1, 2, 3]
        :echo mylist[2:8]               " result: [2, 3]

NOTE: mylist[s:e] means using the variable "s:e" as index.  Watch out for
using a single letter variable before the ":".  Insert a space when needed:
mylist[s : e].


List identity 
                                                        list-identity
When variable "aa" is a list and you assign it to another variable "bb", both
variables refer to the same list.  Thus changing the list "aa" will also
change "bb": 
        :let aa = [1, 2, 3]
        :let bb = aa
        :call add(aa, 4)
        :echo bb
       [1, 2, 3, 4]

Making a copy of a list is done with the copy() function.  Using [:] also
works, as explained above.  This creates a shallow copy of the list: Changing
a list item in the list will also change the item in the copied list: 
        :let aa = [[1, 'a'], 2, 3]
        :let bb = copy(aa)
        :call add(aa, 4)
        :let aa[0][1] = 'aaa'
        :echo aa
       [[1, aaa], 2, 3, 4] 
        :echo bb
       [[1, aaa], 2, 3]

To make a completely independent list use deepcopy().  This also makes a
copy of the values in the list, recursively.  Up to a hundred levels deep.

The operator "is" can be used to check if two variables refer to the same
List.  "isnot" does the opposite.  In contrast "==" compares if two lists have
the same value. 
        :let alist = [1, 2, 3]
        :let blist = [1, 2, 3]
        :echo alist is blist
       0 
        :echo alist == blist
       1

Note about comparing lists: Two lists are considered equal if they have the
same length and all items compare equal, as with using "==".  There is one
exception: When comparing a number with a string they are considered
different.  There is no automatic type conversion, as with using "==" on
variables.  Example: 
        echo 4 == "4"
       1 
        echo [4] == ["4"]
       0

Thus comparing Lists is more strict than comparing numbers and strings.  You
can compare simple values this way too by putting them in a list: 

        :let a = 5
        :let b = "5"
        :echo a == b
       1 
        :echo [a] == [b]
       0


List unpack 

To unpack the items in a list to individual variables, put the variables in
square brackets, like list items: 
        :let [var1, var2] = mylist

When the number of variables does not match the number of items in the list
this produces an error.  To handle any extra items from the list append ";"
and a variable name: 
        :let [var1, var2; rest] = mylist

This works like: 
        :let var1 = mylist[0]
        :let var2 = mylist[1]
        :let rest = mylist[2:]

Except that there is no error if there are only two items.  "rest" will be an
empty list then.


List modification 
                                                        list-modification
To change a specific item of a list use :let this way: 
        :let list[4] = "four"
        :let listlist[0][3] = item

To change part of a list you can specify the first and last item to be
modified.  The value must at least have the number of items in the range: 
        :let list[3:5] = [3, 4, 5]

Adding and removing items from a list is done with functions.  Here are a few
examples: 
        :call insert(list, 'a')         " prepend item 'a'
        :call insert(list, 'a', 3)      " insert item 'a' before list[3]
        :call add(list, "new")          " append String item
        :call add(list, [1, 2])         " append a List as one new item
        :call extend(list, [1, 2])      " extend the list with two more items
        :let i = remove(list, 3)        " remove item 3
        :unlet list[3]                  " idem
        :let l = remove(list, 3, -1)    " remove items 3 to last item
        :unlet list[3 : ]               " idem
        :call filter(list, 'v:val !~ "x"')  " remove items with an 'x'

Changing the order of items in a list: 
        :call sort(list)                " sort a list alphabetically
        :call reverse(list)             " reverse the order of items
        :call uniq(sort(list))          " sort and remove duplicates


For loop 

The :for loop executes commands for each item in a List, String or Blob.
A variable is set to each item in sequence.  Example with a List: 
        :for item in mylist
        :   call Doit(item)
        :endfor

This works like: 
        :let index = 0
        :while index < len(mylist)
        :   let item = mylist[index]
        :   :call Doit(item)
        :   let index = index + 1
        :endwhile

If all you want to do is modify each item in the list then the map()
function will be a simpler method than a for loop.

Just like the :let command, :for also accepts a list of variables.  This
requires the argument to be a List of Lists. 
        :for [lnum, col] in [[1, 3], [2, 8], [3, 0]]
        :   call Doit(lnum, col)
        :endfor

This works like a :let command is done for each list item.  Again, the types
must remain the same to avoid an error.

It is also possible to put remaining items in a List variable: 
        :for [i, j; rest] in listlist
        :   call Doit(i, j)
        :   if !empty(rest)
        :      echo "remainder: " .. string(rest)
        :   endif
        :endfor

For a Blob one byte at a time is used.

For a String one character, including any composing characters, is used as a
String.  Example: 
        for c in text
          echo 'This character is ' .. c
        endfor


List functions 
                                                E714
Functions that are useful with a List: 
        :let r = call(funcname, list)   " call a function with an argument list
        :if empty(list)                 " check if list is empty
        :let l = len(list)              " number of items in list
        :let big = max(list)            " maximum value in list
        :let small = min(list)          " minimum value in list
        :let xs = count(list, 'x')      " count nr of times 'x' appears in list
        :let i = index(list, 'x')       " index of first 'x' in list
        :let lines = getline(1, 10)     " get ten text lines from buffer
        :call append('$', lines)        " append text lines in buffer
        :let list = split("a b c")      " create list from items in a string
        :let string = join(list, ', ')  " create string from list items
        :let s = string(list)           " String representation of list
        :call map(list, '">> " .. v:val')  " prepend ">> " to each item

Don't forget that a combination of features can make things simple.  For
example, to add up all the numbers in a list: 
        :exe 'let sum = ' .. join(nrlist, '+')


1.4 Dictionaries 
                                dict Dict Dictionaries Dictionary
A Dictionary is an associative array: Each entry has a key and a value.  The
entry can be located with the key.  The entries are stored without a specific
ordering.


Dictionary creation 
                                                E720 E721 E722 E723
A Dictionary is created with a comma-separated list of entries in curly
braces.  Each entry has a key and a value, separated by a colon.  Each key can
only appear once.  Examples: 
        :let mydict = {1: 'one', 2: 'two', 3: 'three'}
        :let emptydict = {}
                                                       E713 E716 E717
A key is always a String.  You can use a Number, it will be converted to a
String automatically.  Thus the String '4' and the number 4 will find the same
entry.  Note that the String '04' and the Number 04 are different, since the
Number will be converted to the String '4', leading zeros are dropped.  The
empty string can also be used as a key.

In Vim9 script literaly keys can be used if the key consists of alphanumeric
characters, underscore and dash, see vim9-literal-dict.
                                                literal-Dict #{}
To avoid having to put quotes around every key the #{} form can be used in
legacy script.  This does require the key to consist only of ASCII letters,
digits, '-' and '_'.  Example: 
        :let mydict = #{zero: 0, one_key: 1, two-key: 2, 333: 3}
Note that 333 here is the string "333".  Empty keys are not possible with #{}.
In Vim9 script the #{} form cannot be used because it can be confused with
the start of a comment.

A value can be any expression.  Using a Dictionary for a value creates a
nested Dictionary: 
        :let nestdict = {1: {11: 'a', 12: 'b'}, 2: {21: 'c'}}

An extra comma after the last entry is ignored.


Accessing entries 

The normal way to access an entry is by putting the key in square brackets: 
        :let val = mydict["one"]
        :let mydict["four"] = 4

You can add new entries to an existing Dictionary this way, unlike Lists.

For keys that consist entirely of letters, digits and underscore the following
form can be used expr-entry: 
        :let val = mydict.one
        :let mydict.four = 4

Since an entry can be any type, also a List and a Dictionary, the indexing and
key lookup can be repeated: 
        :echo dict.key[idx].key


Dictionary to List conversion 

You may want to loop over the entries in a dictionary.  For this you need to
turn the Dictionary into a List and pass it to :for.

Most often you want to loop over the keys, using the keys() function: 
        :for key in keys(mydict)
        :   echo key .. ': ' .. mydict[key]
        :endfor

The List of keys is unsorted.  You may want to sort them first: 
        :for key in sort(keys(mydict))

To loop over the values use the values() function:  
        :for v in values(mydict)
        :   echo "value: " .. v
        :endfor

If you want both the key and the value use the items() function.  It returns
a List in which each item is a List with two items, the key and the value: 
        :for [key, value] in items(mydict)
        :   echo key .. ': ' .. value
        :endfor


Dictionary identity 
                                                        dict-identity
Just like Lists you need to use copy() and deepcopy() to make a copy of a
Dictionary.  Otherwise, assignment results in referring to the same
Dictionary: 
        :let onedict = {'a': 1, 'b': 2}
        :let adict = onedict
        :let adict['a'] = 11
        :echo onedict['a']
        11

Two Dictionaries compare equal if all the key-value pairs compare equal.  For
more info see list-identity.


Dictionary modification 
                                                        dict-modification
To change an already existing entry of a Dictionary, or to add a new entry,
use :let this way: 
        :let dict[4] = "four"
        :let dict['one'] = item

Removing an entry from a Dictionary is done with remove() or :unlet.
Three ways to remove the entry with key "aaa" from dict: 
        :let i = remove(dict, 'aaa')
        :unlet dict.aaa
        :unlet dict['aaa']

Merging a Dictionary with another is done with extend(): 
        :call extend(adict, bdict)
This extends adict with all entries from bdict.  Duplicate keys cause entries
in adict to be overwritten.  An optional third argument can change this.
Note that the order of entries in a Dictionary is irrelevant, thus don't
expect ":echo adict" to show the items from bdict after the older entries in
adict.

Weeding out entries from a Dictionary can be done with filter(): 
        :call filter(dict, 'v:val =~ "x"')
This removes all entries from "dict" with a value not matching 'x'.
This can also be used to remove all entries: 
        call filter(dict, 0)


Dictionary function 
                                Dictionary-function self E725 E862
When a function is defined with the "dict" attribute it can be used in a
special way with a dictionary.  Example: 
        :function Mylen() dict
        :   return len(self.data)
        :endfunction
        :let mydict = {'data': [0, 1, 2, 3], 'len': function("Mylen")}
        :echo mydict.len()

This is like a method in object oriented programming.  The entry in the
Dictionary is a Funcref.  The local variable "self" refers to the dictionary
the function was invoked from.

It is also possible to add a function without the "dict" attribute as a
Funcref to a Dictionary, but the "self" variable is not available then.

                                numbered-function anonymous-function
To avoid the extra name for the function it can be defined and directly
assigned to a Dictionary in this way: 
        :let mydict = {'data': [0, 1, 2, 3]}
        :function mydict.len()
        :   return len(self.data)
        :endfunction
        :echo mydict.len()

The function will then get a number and the value of dict.len is a Funcref
that references this function.  The function can only be used through a
Funcref.  It will automatically be deleted when there is no Funcref
remaining that refers to it.

It is not necessary to use the "dict" attribute for a numbered function.

If you get an error for a numbered function, you can find out what it is with
a trick.  Assuming the function is 42, the command is: 
        :function g:42


Functions for Dictionaries 
                                                        E715
Functions that can be used with a Dictionary: 
        :if has_key(dict, 'foo')        " TRUE if dict has entry with key "foo"
        :if empty(dict)                 " TRUE if dict is empty
        :let l = len(dict)              " number of items in dict
        :let big = max(dict)            " maximum value in dict
        :let small = min(dict)          " minimum value in dict
        :let xs = count(dict, 'x')      " count nr of times 'x' appears in dict
        :let s = string(dict)           " String representation of dict
        :call map(dict, '">> " .. v:val')  " prepend ">> " to each item


1.5 Blobs 
                                                blob Blob Blobs E978
A Blob is a binary object.  It can be used to read an image from a file and
send it over a channel, for example.

A Blob mostly behaves like a List of numbers, where each number has the
value of an 8-bit byte, from 0 to 255.


Blob creation 

A Blob can be created with a blob-literal: 
        :let b = 0zFF00ED015DAF
Dots can be inserted between bytes (pair of hex characters) for readability,
they don't change the value: 
        :let b = 0zFF00.ED01.5DAF

A blob can be read from a file with readfile() passing the {type} argument
set to "B", for example: 
        :let b = readfile('image.png', 'B')

A blob can be read from a channel with the ch_readblob() function.


Blob index 
                                                        blob-index E979
A byte in the Blob can be accessed by putting the index in square brackets
after the Blob.  Indexes are zero-based, thus the first byte has index zero. 
        :let myblob = 0z00112233
        :let byte = myblob[0]           " get the first byte: 0x00
        :let byte = myblob[2]           " get the third byte: 0x22

A negative index is counted from the end.  Index -1 refers to the last byte in
the Blob, -2 to the last but one byte, etc. 
        :let last = myblob[-1]          " get the last byte: 0x33

To avoid an error for an invalid index use the get() function.  When an item
is not available it returns -1 or the default value you specify: 
        :echo get(myblob, idx)
        :echo get(myblob, idx, 999)


Blob iteration 

The :for loop executes commands for each byte of a Blob.  The loop variable is
set to each byte in the Blob.  Example: 
        :for byte in 0z112233
        :   call Doit(byte)
        :endfor
This calls Doit() with 0x11, 0x22 and 0x33.


Blob concatenation 

Two blobs can be concatenated with the "+" operator: 
        :let longblob = myblob + 0z4455
        :let myblob += 0z6677

To change a blob in-place see blob-modification below.


Part of a blob 

A part of the Blob can be obtained by specifying the first and last index,
separated by a colon in square brackets: 
        :let myblob = 0z00112233
        :let shortblob = myblob[1:2]    " get 0z1122
        :let shortblob = myblob[2:-1]   " get 0z2233

Omitting the first index is similar to zero.  Omitting the last index is
similar to -1. 
        :let endblob = myblob[2:]       " from item 2 to the end: 0z2233
        :let shortblob = myblob[2:2]    " Blob with one byte: 0z22
        :let otherblob = myblob[:]      " make a copy of the Blob

If the first index is beyond the last byte of the Blob or the second index is
before the first index, the result is an empty Blob.  There is no error
message.

If the second index is equal to or greater than the length of the list the
length minus one is used: 
        :echo myblob[2:8]               " result: 0z2233


Blob modification 
                                        blob-modification E1182 E1184
To change a specific byte of a blob use :let this way: 
        :let blob[4] = 0x44

When the index is just one beyond the end of the Blob, it is appended. Any
higher index is an error.

To change a sequence of bytes the [:] notation can be used: 
        let blob[1:3] = 0z445566
The length of the replaced bytes must be exactly the same as the value
provided. E972

To change part of a blob you can specify the first and last byte to be
modified.  The value must have the same number of bytes in the range: 
        :let blob[3:5] = 0z334455

You can also use the functions add(), remove() and insert().


Blob identity 

Blobs can be compared for equality: 
        if blob == 0z001122
And for equal identity: 
        if blob is otherblob
                                                       blob-identity E977
When variable "aa" is a Blob and you assign it to another variable "bb", both
variables refer to the same Blob.  Then the "is" operator returns true.

When making a copy using [:] or copy() the values are the same, but the
identity is different: 
        :let blob = 0z112233
        :let blob2 = blob
        :echo blob == blob2
       1 
        :echo blob is blob2
       1 
        :let blob3 = blob[:]
        :echo blob == blob3
       1 
        :echo blob is blob3
       0

Making a copy of a Blob is done with the copy() function.  Using [:] also
works, as explained above.


1.6 More about variables 
                                                        more-variables
If you need to know the type of a variable or expression, use the type()
function.

When the '!' flag is included in the 'viminfo' option, global variables that
start with an uppercase letter, and don't contain a lowercase letter, are
stored in the viminfo file viminfo-file.

When the 'sessionoptions' option contains "global", global variables that
start with an uppercase letter and contain at least one lowercase letter are
stored in the session file session-file.

variable name           can be stored where 
my_var_6                not
My_Var_6                session file
MY_VAR_6                viminfo file


In legacy script it is possible to form a variable name with curly braces, see
curly-braces-names.

==============================================================================
2. Expression syntax                                    expression-syntax
                                                        E1143
Expression syntax summary, from least to most significant:

expr1 expr2
        expr2 ? expr1 : expr1   if-then-else

expr2 expr3
        expr3 || expr3 ...      logical OR

expr3 expr4
        expr4 && expr4 ...      logical AND

expr4 expr5
        expr5 == expr5          equal
        expr5 != expr5          not equal
        expr5 >  expr5          greater than
        expr5 >= expr5          greater than or equal
        expr5 <  expr5          smaller than
        expr5 <= expr5          smaller than or equal
        expr5 =~ expr5          regexp matches
        expr5 !~ expr5          regexp doesn't match

        expr5 ==? expr5         equal, ignoring case
        expr5 ==# expr5         equal, match case
        etc.                    As above, append ? for ignoring case, # for
                                matching case

        expr5 is expr5          same List, Dictionary or Blob instance
        expr5 isnot expr5       different List, Dictionary or Blob
                                instance

expr5 expr6
        expr6 +  expr6 ...      number addition, list or blob concatenation
        expr6 -  expr6 ...      number subtraction
        expr6 .  expr6 ...      string concatenation
        expr6 .. expr6 ...      string concatenation

expr6 expr7
        expr7 *  expr7 ...      number multiplication
        expr7 /  expr7 ...      number division
        expr7 %  expr7 ...      number modulo

expr7 expr8
        <type>expr8             type check and conversion (Vim9 only)

expr8 expr9
        ! expr8                 logical NOT
        - expr8                 unary minus
        + expr8                 unary plus

expr9 expr10
        expr9[expr1]            byte of a String or item of a List
        expr9[expr1 : expr1]    substring of a String or sublist of a List
        expr9.name              entry in a Dictionary
        expr9(expr1, ...)       function call with Funcref variable
        expr9->name(expr1, ...) method call

expr10  number                number constant
        "string"                string constant, backslash is special
        'string'                string constant, ' is doubled
        [expr1, ...]            List
        {expr1: expr1, ...}     Dictionary
        #{key: expr1, ...}      legacy Dictionary
        &option                 option value
        (expr1)                 nested expression
        variable                internal variable
        va{ria}ble              internal variable with curly braces
        $VAR                    environment variable
        @r                      contents of register 'r'
        function(expr1, ...)    function call
        func{ti}on(expr1, ...)  function call with curly braces
        {args -> expr1}         legacy lambda expression
        (args) => expr1         Vim9 lambda expression


"..." indicates that the operations in this level can be concatenated.
Example: 
        &nu || &list && &shell == "csh"

All expressions within one level are parsed from left to right.

Expression nesting is limited to 1000 levels deep (300 when build with MSVC)
to avoid running out of stack and crashing. E1169


expr1                           expr1 ternary falsy-operator ?? E109
-----

The ternary operator: expr2 ? expr1 : expr1
The falsy operator:   expr2 ?? expr1

Ternary operator 

In legacy script the expression before the '?' is evaluated to a number.  If
it evaluates to TRUE, the result is the value of the expression between the
'?' and ':', otherwise the result is the value of the expression after the
':'.

In Vim9 script the first expression must evaluate to a boolean, see
vim9-boolean.

Example: 
        :echo lnum == 1 ? "top" : lnum

Since the first expression is an "expr2", it cannot contain another ?:.  The
other two expressions can, thus allow for recursive use of ?:.
Example: 
        :echo lnum == 1 ? "top" : lnum == 1000 ? "last" : lnum

To keep this readable, using line-continuation is suggested: 
        :echo lnum == 1
        :\      ? "top"
        :\      : lnum == 1000
        :\              ? "last"
        :\              : lnum

You should always put a space before the ':', otherwise it can be mistaken for
use in a variable such as "a:1".

Falsy operator 

This is also known as the "null coalescing operator", but that's too
complicated, thus we just call it the falsy operator.

The expression before the '??' is evaluated.  If it evaluates to
truthy, this is used as the result.  Otherwise the expression after the '??'
is evaluated and used as the result.  This is most useful to have a default
value for an expression that may result in zero or empty: 
        echo theList ?? 'list is empty'
        echo GetName() ?? 'unknown'

These are similar, but not equal: 
        expr2 ?? expr1
        expr2 ? expr2 : expr1
In the second line "expr2" is evaluated twice.  And in Vim9 script the type
of expr2 before "?" must be a boolean.


expr2 and expr3                                         expr2 expr3
---------------

expr3 || expr3 ..       logical OR              expr-barbar
expr4 && expr4 ..       logical AND             expr-&&

The "||" and "&&" operators take one argument on each side.

In legacy script the arguments are (converted to) Numbers.

In Vim9 script the values must be boolean, see vim9-boolean.  Use "!!" to
convert any type to a boolean.

The result is:
    input                        output 
n1      n2              n1 || n2        n1 && n2 
FALSE FALSE         FALSE         FALSE
FALSE TRUE          TRUE          FALSE
TRUE  FALSE         TRUE          FALSE
TRUE  TRUE          TRUE          TRUE

The operators can be concatenated, for example: 

        &nu || &list && &shell == "csh"

Note that "&&" takes precedence over "||", so this has the meaning of: 

        &nu || (&list && &shell == "csh")

Once the result is known, the expression "short-circuits", that is, further
arguments are not evaluated.  This is like what happens in C.  For example: 

        let a = 1
        echo a || b

This is valid even if there is no variable called "b" because "a" is TRUE,
so the result must be TRUE.  Similarly below: 

        echo exists("b") && b == "yes"

This is valid whether "b" has been defined or not.  The second clause will
only be evaluated if "b" has been defined.


expr4                                                   expr4 E1153
-----

expr5 {cmp} expr5

Compare two expr5 expressions.  In legacy script the result is a 0 if it
evaluates to false, or 1 if it evaluates to true.  In Vim9 script the result
is true or false.

                        expr-==  expr-!=  expr->   expr->=
                        expr-<   expr-<=  expr-=~  expr-!~
                        expr-==# expr-!=# expr->#  expr->=#
                        expr-<#  expr-<=# expr-=~# expr-!~#
                        expr-==? expr-!=? expr->?  expr->=?
                        expr-<?  expr-<=? expr-=~? expr-!~?
                        expr-is expr-isnot expr-is# expr-isnot#
                        expr-is? expr-isnot? E1072
                use 'ignorecase'    match case     ignore case 
equal                   ==              ==#             ==?
not equal               !=              !=#             !=?
greater than            >               >#              >?
greater than or equal   >=              >=#             >=?
smaller than            <               <#              <?
smaller than or equal   <=              <=#             <=?
regexp matches          =~              =~#             =~?
regexp doesn't match    !~              !~#             !~?
same instance           is              is#             is?
different instance      isnot           isnot#          isnot?

Examples:
"abc" ==# "Abc"   evaluates to 0
"abc" ==? "Abc"   evaluates to 1
"abc" == "Abc"    evaluates to 1 if 'ignorecase' is set, 0 otherwise
NOTE: In Vim9 script 'ignorecase' is not used.

                                                        E691 E692
A List can only be compared with a List and only "equal", "not equal",
"is" and "isnot" can be used.  This compares the values of the list,
recursively.  Ignoring case means case is ignored when comparing item values.

                                                        E735 E736
A Dictionary can only be compared with a Dictionary and only "equal", "not
equal", "is" and "isnot" can be used.  This compares the key/values of the
Dictionary recursively.  Ignoring case means case is ignored when comparing
item values.

                                                        E694
A Funcref can only be compared with a Funcref and only "equal", "not
equal", "is" and "isnot" can be used.  Case is never ignored.  Whether
arguments or a Dictionary are bound (with a partial) matters.  The
Dictionaries must also be equal (or the same, in case of "is") and the
arguments must be equal (or the same).

To compare Funcrefs to see if they refer to the same function, ignoring bound
Dictionary and arguments, use get() to get the function name: 
        if get(Part1, 'name') == get(Part2, 'name')
           " Part1 and Part2 refer to the same function
                                                       E1037
Using "is" or "isnot" with a List, Dictionary or Blob checks whether
the expressions are referring to the same List, Dictionary or Blob
instance.  A copy of a List is different from the original List.  When
using "is" without a List, Dictionary or Blob, it is equivalent to
using "equal", using "isnot" equivalent to using "not equal".  Except that
a different type means the values are different: 
        echo 4 == '4'
        1
        echo 4 is '4'
        0
        echo 0 is []
        0
"is#"/"isnot#" and "is?"/"isnot?" can be used to match and ignore case.

In legacy script, when comparing a String with a Number, the String is
converted to a Number, and the comparison is done on Numbers.  This means
that: 
        echo 0 == 'x'
        1
because 'x' converted to a Number is zero.  However: 
        echo [0] == ['x']
        0
Inside a List or Dictionary this conversion is not used.

In Vim9 script the types must match.

When comparing two Strings, this is done with strcmp() or stricmp().  This
results in the mathematical difference (comparing byte values), not
necessarily the alphabetical difference in the local language.

When using the operators with a trailing '#', or the short version and
'ignorecase' is off, the comparing is done with strcmp(): case matters.

When using the operators with a trailing '?', or the short version and
'ignorecase' is set, the comparing is done with stricmp(): case is ignored.

'smartcase' is not used.

The "=~" and "!~" operators match the lefthand argument with the righthand
argument, which is used as a pattern.  See pattern for what a pattern is.
This matching is always done like 'magic' was set and 'cpoptions' is empty, no
matter what the actual value of 'magic' or 'cpoptions' is.  This makes scripts
portable.  To avoid backslashes in the regexp pattern to be doubled, use a
single-quote string, see literal-string.
Since a string is considered to be a single line, a multi-line pattern
(containing \n, backslash-n) will not match.  However, a literal NL character
can be matched like an ordinary character.  Examples:
        "foo\nbar" =~ "\n"      evaluates to 1
        "foo\nbar" =~ "\\n"     evaluates to 0


expr5 and expr6                         expr5 expr6 E1036 E1051
---------------
expr6 + expr6   Number addition, List or Blob concatenation expr-+
expr6 - expr6   Number subtraction                              expr--
expr6 . expr6   String concatenation                            expr-.
expr6 .. expr6  String concatenation                            expr-..

For Lists only "+" is possible and then both expr6 must be a list.  The
result is a new list with the two lists Concatenated.

For String concatenation ".." is preferred, since "." is ambiguous, it is also
used for Dict member access and floating point numbers.
In Vim9 script and when vimscript-version is 2 or higher, using "." is not
allowed.

In Vim9 script the arguments of ".." are converted to String for simple
types: Number, Float, Special and Bool.  For other types string() should be
used.

expr7 * expr7  Number multiplication                            expr-star
expr7 / expr7  Number division                                  expr-/
expr7 % expr7  Number modulo                                    expr-%

In legacy script, for all operators except "." and "..", Strings are converted
to Numbers.

For bitwise operators see and(), or() and xor().

Note the difference between "+" and ".." in legacy script:
        "123" + "456" = 579
        "123" .. "456" = "123456"

Since '..' has the same precedence as '+' and '-', you need to read: 
        1 .. 90 + 90.0
As: 
        (1 .. 90) + 90.0
That works in legacy script, since the String "190" is automatically converted
to the Number 190, which can be added to the Float 90.0.  However: 
        1 .. 90 * 90.0
Should be read as: 
        1 .. (90 * 90.0)
Since '..' has lower precedence than '*'.  This does NOT work, since this
attempts to concatenate a Float and a String.

When dividing a Number by zero the result depends on the value:
          0 / 0  = -0x80000000  (like NaN for Float)
         >0 / 0  =  0x7fffffff  (like positive infinity)
         <0 / 0  = -0x7fffffff  (like negative infinity)
        (before Vim 7.2 it was always 0x7fffffff)
In Vim9 script dividing a number by zero is an error. E1154

When 64-bit Number support is enabled:
          0 / 0  = -0x8000000000000000  (like NaN for Float)
         >0 / 0  =  0x7fffffffffffffff  (like positive infinity)
         <0 / 0  = -0x7fffffffffffffff  (like negative infinity)

When the righthand side of '%' is zero, the result is 0.

None of these work for Funcrefs.

".", ".." and "%" do not work for Float. E804 E1035


expr7                                                   expr7
-----
<type>expr8

This is only available in Vim9 script, see type-casting.


expr8                                                   expr8
-----
! expr8                 logical NOT             expr-!
- expr8                 unary minus             expr-unary--
+ expr8                 unary plus              expr-unary-+

For '!' TRUE becomes FALSE, FALSE becomes TRUE (one).
For '-' the sign of the number is changed.
For '+' the number is unchanged.  Note: "++" has no effect.

In legacy script a String will be converted to a Number first.  Note that if
the string does not start with a digit you likely don't get what you expect.

In Vim9 script an error is given when "-" or "+" is used and the type is not
a number.

In Vim9 script "!" can be used for any type and the result is always a
boolean.  Use "!!" to convert any type to a boolean, according to whether the
value is falsy.

These three can be repeated and mixed.  Examples:
        !-1         == 0
        !!8         == 1
        --9         == 9


expr9                                                   expr9
-----
This expression is either expr10 or a sequence of the alternatives below,
in any order.  E.g., these are all possible:
        expr9[expr1].name
        expr9.name[expr1]
        expr9(expr1, ...)[expr1].name
        expr9->(expr1, ...)[expr1]
Evaluation is always from left to right.

expr9[expr1]            item of String or List        expr-[] E111
                                                E909 subscript E1062
In legacy Vim script:
If expr9 is a Number or String this results in a String that contains the
expr1'th single byte from expr9.  expr9 is used as a String (a number is
automatically converted to a String), expr1 as a Number.  This doesn't
recognize multibyte encodings, see byteidx() for an alternative, or use
split() to turn the string into a list of characters.  Example, to get the
byte under the cursor: 
        :let c = getline(".")[col(".") - 1]

In Vim9 script:                                       E1147 E1148
If expr9 is a String this results in a String that contains the expr1'th
single character (including any composing characters) from expr9.  To use byte
indexes use strpart().

Index zero gives the first byte or character.  Careful: text column numbers
start with one!

If the length of the String is less than the index, the result is an empty
String.  A negative index always results in an empty string (reason: backward
compatibility).  Use [-1:] to get the last byte or character.
In Vim9 script a negative index is used like with a list: count from the end.

If expr9 is a List then it results the item at index expr1.  See list-index
for possible index values.  If the index is out of range this results in an
error.  Example: 
        :let item = mylist[-1]          " get last item

Generally, if a List index is equal to or higher than the length of the
List, or more negative than the length of the List, this results in an
error.


expr9[expr1a : expr1b]  substring or sublist            expr-[:]

If expr9 is a String this results in the substring with the bytes or
characters from expr1a to and including expr1b.  expr9 is used as a String,
expr1a and expr1b are used as a Number.

In legacy Vim script the indexes are byte indexes.  This doesn't recognize
multibyte encodings, see byteidx() for computing the indexes.  If expr9 is
a Number it is first converted to a String.

In Vim9 script the indexes are character indexes and include composing
characters.  To use byte indexes use strpart().  To use character indexes
without including composing characters use strcharpart().

The item at index expr1b is included, it is inclusive.  For an exclusive index
use the slice() function.

If expr1a is omitted zero is used.  If expr1b is omitted the length of the
string minus one is used.

A negative number can be used to measure from the end of the string.  -1 is
the last character, -2 the last but one, etc.

If an index goes out of range for the string characters are omitted.  If
expr1b is smaller than expr1a the result is an empty string.

Examples: 
        :let c = name[-1:]              " last byte of a string
        :let c = name[0:-1]             " the whole string
        :let c = name[-2:-2]            " last but one byte of a string
        :let s = line(".")[4:]          " from the fifth byte to the end
        :let s = s[:-3]                 " remove last two bytes

                                                        slice
If expr9 is a List this results in a new List with the items indicated by
the indexes expr1a and expr1b.  This works like with a String, as explained
just above. Also see sublist below.  Examples: 
        :let l = mylist[:3]             " first four items
        :let l = mylist[4:4]            " List with one item
        :let l = mylist[:]              " shallow copy of a List

If expr9 is a Blob this results in a new Blob with the bytes in the
indexes expr1a and expr1b, inclusive.  Examples: 
        :let b = 0zDEADBEEF
        :let bs = b[1:2]                " 0zADBE
        :let bs = b[:]                  " copy of 0zDEADBEEF

Using expr9[expr1] or expr9[expr1a : expr1b] on a Funcref results in an
error.

Watch out for confusion between a namespace and a variable followed by a colon
for a sublist: 
        mylist[n:]     " uses variable n
        mylist[s:]     " uses namespace s:, error!


expr9.name              entry in a Dictionary         expr-entry
                                                        E1203 E1229
If expr9 is a Dictionary and it is followed by a dot, then the following
name will be used as a key in the Dictionary.  This is just like:
expr9[name].

The name must consist of alphanumeric characters, just like a variable name,
but it may start with a number.  Curly braces cannot be used.

There must not be white space before or after the dot.

Examples: 
        :let dict = {"one": 1, 2: "two"}
        :echo dict.one          " shows "1"
        :echo dict.2            " shows "two"
        :echo dict .2           " error because of space before the dot

Note that the dot is also used for String concatenation.  To avoid confusion
always put spaces around the dot for String concatenation.


expr9(expr1, ...)       Funcref function call         E1085

When expr9 is a Funcref type variable, invoke the function it refers to.


expr9->name([args])     method call                     method ->
expr9->{lambda}([args])
                                                        E260 E276 E1265
For methods that are also available as global functions this is the same as: 
        name(expr9 [, args])
There can also be methods specifically for the type of "expr9".

This allows for chaining, passing the value that one method returns to the
next method: 
        mylist->filter(filterexpr)->map(mapexpr)->sort()->join()

Example of using a lambda: 
        GetPercentage()->{x -> x * 100}()->printf('%d%%')

When using -> the expr8 operators will be applied first, thus: 
        -1.234->string()
Is equivalent to: 
        (-1.234)->string()
And NOT: 
        -(1.234->string())

What comes after "->" can be a name, a simple expression (not containing any
parenthesis), or any expression in parentheses: 
        base->name(args)
        base->some.name(args)
        base->alist[idx](args)
        base->(getFuncRef())(args)
Note that in the last call the base is passed to the function resulting from
"(getFuncRef())", inserted before "args".

                                                        E274
"->name(" must not contain white space.  There can be white space before the
"->" and after the "(", thus you can split the lines like this: 
        mylist
        \ ->filter(filterexpr)
        \ ->map(mapexpr)
        \ ->sort()
        \ ->join()

When using the lambda form there must be no white space between the } and the
(.


                                                        expr10
number
------
number                  number constant                 expr-number

                        0x hex-number 0o octal-number binary-number
Decimal, Hexadecimal (starting with 0x or 0X), Binary (starting with 0b or 0B)
and Octal (starting with 0, 0o or 0O).

                                                floating-point-format
Floating point numbers can be written in two forms:

        [-+]{N}.{M}
        [-+]{N}.{M}[eE][-+]{exp}

{N} and {M} are numbers.  Both {N} and {M} must be present and can only
contain digits, except that in Vim9 script in {N} single quotes between
digits are ignored.
[-+] means there is an optional plus or minus sign.
{exp} is the exponent, power of 10.
Only a decimal point is accepted, not a comma.  No matter what the current
locale is.
{only when compiled with the |+float| feature}

Examples:
        123.456
        +0.0001
        55.0
        -0.123
        1.234e03
        1.0E-6
        -3.1416e+88

These are INVALID:
        3.              empty {M}
        1e40            missing .{M}

Rationale:
Before floating point was introduced, the text "123.456" was interpreted as
the two numbers "123" and "456", both converted to a string and concatenated,
resulting in the string "123456".  Since this was considered pointless, and we
could not find it intentionally being used in Vim scripts, this backwards
incompatibility was accepted in favor of being able to use the normal notation
for floating point numbers.

                                                        float-pi float-e
A few useful values to copy&paste: 
        :let pi = 3.14159265359
        :let e  = 2.71828182846
Or, if you don't want to write them in as floating-point literals, you can
also use functions, like the following: 
        :let pi = acos(-1.0)
        :let e  = exp(1.0)

                                                floating-point-precision
The precision and range of floating points numbers depends on what "double"
means in the library Vim was compiled with.  There is no way to change this at
runtime.

The default for displaying a Float is to use 6 decimal places, like using
printf("%g", f).  You can select something else when using the printf()
function.  Example: 
        :echo printf('%.15e', atan(1))
       7.853981633974483e-01



string                                  string String expr-string E114
------
"string"                string constant         expr-quote

Note that double quotes are used.

A string constant accepts these special characters:
\...    three-digit octal number (e.g., "\316")
\..     two-digit octal number (must be followed by non-digit)
\.      one-digit octal number (must be followed by non-digit)
\x..    byte specified with two hex numbers (e.g., "\x1f")
\x.     byte specified with one hex number (must be followed by non-hex char)
\X..    same as \x..
\X.     same as \x.
\u....  character specified with up to 4 hex numbers, stored according to the
        current value of 'encoding' (e.g., "\u02a4")
\U....  same as \u but allows up to 8 hex numbers.
\b      backspace <BS>
\e      escape <Esc>
\f      formfeed 0x0C
\n      newline <NL>
\r      return <CR>
\t      tab <Tab>
\\      backslash
\"      double quote
\<xxx>  Special key named "xxx".  e.g. "\<C-W>" for CTRL-W.  This is for use
        in mappings, the 0x80 byte is escaped.
        To use the double quote character it must be escaped: "<M-\">".
        Don't use <Char-xxxx> to get a UTF-8 character, use \uxxxx as
        mentioned above.
\<*xxx> Like \<xxx> but prepends a modifier instead of including it in the
        character.  E.g. "\<C-w>" is one character 0x17 while "\<*C-w>" is four
        bytes: 3 for the CTRL modifier and then character "W".

Note that "\xff" is stored as the byte 255, which may be invalid in some
encodings.  Use "\u00ff" to store character 255 according to the current value
of 'encoding'.

Note that "\000" and "\x00" force the end of the string.


blob-literal                            blob-literal E973
------------

Hexadecimal starting with 0z or 0Z, with an arbitrary number of bytes.
The sequence must be an even number of hex characters.  Example: 
        :let b = 0zFF00ED015DAF


literal-string                                          literal-string E115
---------------
'string'                string constant                 expr-'

Note that single quotes are used.

This string is taken as it is.  No backslashes are removed or have a special
meaning.  The only exception is that two quotes stand for one quote.

Single quoted strings are useful for patterns, so that backslashes do not need
to be doubled.  These two commands are equivalent: 
        if a =~ "\\s*"
        if a =~ '\s*'


interpolated-string                                     interp-string E256
--------------------
$"string"               interpolated string constant            expr-$quote
$'string'               interpolated literal string constant    expr-$'

Interpolated strings are an extension of the string and literal-string,
allowing the inclusion of Vim script expressions (see expr1).  Any
expression returning a value can be enclosed between curly braces.  The value
is converted to a string.  All the text and results of the expressions
are concatenated to make a new string.
                                                                E1278
To include an opening brace '{' or closing brace '}' in the string content
double it.  For double quoted strings using a backslash also works.  A single
closing brace '}' will result in an error.

Examples: 
        let your_name = input("What's your name? ")
       What's your name?  Peter 

        echo
        echo $"Hello, {your_name}!"
       Hello, Peter! 

        echo $"The square root of {{9}} is {sqrt(9)}"
       The square root of {9} is 3.0 


option                                          expr-option E112 E113
------
&option                 option value, local value if possible
&g:option               global option value
&l:option               local option value

Examples: 
        echo "tabstop is " .. &tabstop
        if &insertmode

Any option name can be used here.  See options.  When using the local value
and there is no buffer-local or window-local value, the global value is used
anyway.


register                                                expr-register @r
--------
@r                      contents of register 'r'

The result is the contents of the named register, as a single string.
Newlines are inserted where required.  To get the contents of the unnamed
register use @" or @@.  See registers for an explanation of the available
registers.

When using the '=' register you get the expression itself, not what it
evaluates to.  Use eval() to evaluate it.


nesting                                         expr-nesting E110
-------
(expr1)                 nested expression


environment variable                                    expr-env
--------------------
$VAR                    environment variable

The String value of any environment variable.  When it is not defined, the
result is an empty string.

The functions getenv() and setenv() can also be used and work for
environment variables with non-alphanumeric names.
The function environ() can be used to get a Dict with all environment
variables.


                                                expr-env-expand
Note that there is a difference between using $VAR directly and using
expand("$VAR").  Using it directly will only expand environment variables that
are known inside the current Vim session.  Using expand() will first try using
the environment variables known inside the current Vim session.  If that
fails, a shell will be used to expand the variable.  This can be slow, but it
does expand all variables that the shell knows about.  Example: 
        :echo $shell
        :echo expand("$shell")
The first one probably doesn't echo anything, the second echoes the $shell
variable (if your shell supports it).


internal variable                       expr-variable E1015 E1089
-----------------
variable                internal variable
See below internal-variables.


function call           expr-function E116 E118 E119 E120
-------------
function(expr1, ...)    function call
See below functions.


lambda expression                               expr-lambda lambda
-----------------
{args -> expr1}         legacy lambda expression                E451
(args) => expr1         Vim9 lambda expression

A lambda expression creates a new unnamed function which returns the result of
evaluating expr1.  Lambda expressions differ from user-functions in
the following ways:

1. The body of the lambda expression is an expr1 and not a sequence of Ex
   commands.
2. The prefix "a:" should not be used for arguments.  E.g.: 
        :let F = {arg1, arg2 -> arg1 - arg2}
        :echo F(5, 2)
       3

The arguments are optional.  Example: 
        :let F = {-> 'error function'}
        :echo F('ignored')
       error function

The Vim9 lambda does not only use a different syntax, it also adds type
checking and can be split over multiple lines, see vim9-lambda.

                                                        closure
Lambda expressions can access outer scope variables and arguments.  This is
often called a closure.  Example where "i" and "a:arg" are used in a lambda
while they already exist in the function scope.  They remain valid even after
the function returns: 
        :function Foo(arg)
        :  let i = 3
        :  return {x -> x + i - a:arg}
        :endfunction
        :let Bar = Foo(4)
        :echo Bar(6)
       5

Note that the variables must exist in the outer scope before the lambda is
defined for this to work.  See also :func-closure.

Lambda and closure support can be checked with: 
        if has('lambda')

Examples for using a lambda expression with sort(), map() and filter(): 
        :echo map([1, 2, 3], {idx, val -> val + 1})
       [2, 3, 4] 
        :echo sort([3,7,2,1,4], {a, b -> a - b})
       [1, 2, 3, 4, 7]

The lambda expression is also useful for Channel, Job and timer: 
        :let timer = timer_start(500,
                        \ {-> execute("echo 'Handler called'", "")},
                        \ {'repeat': 3})
       Handler called
        Handler called
        Handler called

Note that it is possible to cause memory to be used and not freed if the
closure is referenced by the context it depends on: 
        function Function()
           let x = 0
           let F = {-> x}
         endfunction
The closure uses "x" from the function scope, and "F" in that same scope
refers to the closure.  This cycle results in the memory not being freed.
Recommendation: don't do this.

Notice how execute() is used to execute an Ex command.  That's ugly though.
In Vim9 script you can use a command block, see inline-function.

Lambda expressions have internal names like '<lambda>42'.  If you get an error
for a lambda expression, you can find what it is with the following command: 
        :function <lambda>42
See also: numbered-function

==============================================================================
3. Internal variable                    internal-variables E461 E1001

An internal variable name can be made up of letters, digits and '_'.  But it
cannot start with a digit.  In legacy script it is also possible to use curly
braces, see curly-braces-names.

In legacy script an internal variable is created with the ":let" command
:let.  An internal variable is explicitly destroyed with the ":unlet"
command :unlet.
Using a name that is not an internal variable or refers to a variable that has
been destroyed results in an error.

In Vim9 script :let is not used and variables work differently, see :var.

                                                variable-scope
There are several name spaces for variables.  Which one is to be used is
specified by what is prepended:

                (nothing) In a function: local to the function;
                          in a legacy script: global;
                          in a Vim9  script: local to the script
buffer-variable    b:   Local to the current buffer.
window-variable    w:   Local to the current window.
tabpage-variable   t:   Local to the current tab page.
global-variable    g:   Global.
local-variable     l:   Local to a function (only in a legacy function)
script-variable    s:   Local to a :source'ed Vim script.
function-argument  a:   Function argument (only in a legacy function).
vim-variable       v:   Global, predefined by Vim.

The scope name by itself can be used as a Dictionary.  For example, to
delete all script-local variables: 
        :for k in keys(s:)
        :    unlet s:[k]
        :endfor

Note: in Vim9 script variables can also be local to a block of commands, see
vim9-scopes.
                                                buffer-variable b:var b:
A variable name that is preceded with "b:" is local to the current buffer.
Thus you can have several "b:foo" variables, one for each buffer.
This kind of variable is deleted when the buffer is wiped out or deleted with
:bdelete.

One local buffer variable is predefined:
                                        b:changedtick changetick
b:changedtick   The total number of changes to the current buffer.  It is
                incremented for each change.  An undo command is also a change
                in this case.  Resetting 'modified' when writing the buffer is
                also counted.
                This can be used to perform an action only when the buffer has
                changed.  Example: 
                    :if my_changedtick != b:changedtick
                    :   let my_changedtick = b:changedtick
                    :   call My_Update()
                    :endif
               You cannot change or delete the b:changedtick variable.

                                                window-variable w:var w:
A variable name that is preceded with "w:" is local to the current window.  It
is deleted when the window is closed.

                                                tabpage-variable t:var t:
A variable name that is preceded with "t:" is local to the current tab page,
It is deleted when the tab page is closed. {not available when compiled
without the +windows feature}

                                                global-variable g:var g:
Inside functions and in Vim9 script global variables are accessed with "g:".
Omitting this will access a variable local to a function or script.  "g:"
can also be used in any other place if you like.

                                                local-variable l:var l:
Inside functions local variables are accessed without prepending anything.
But you can also prepend "l:" if you like.  However, without prepending "l:"
you may run into reserved variable names.  For example "count".  By itself it
refers to "v:count".  Using "l:count" you can have a local variable with the
same name.

                                                script-variable s:var
In a legacy Vim script variables starting with "s:" can be used.  They cannot
be accessed from outside of the scripts, thus are local to the script.
In Vim9 script the "s:" prefix can be omitted, variables are script-local by
default.

They can be used in:
- commands executed while the script is sourced
- functions defined in the script
- autocommands defined in the script
- functions and autocommands defined in functions and autocommands which were
  defined in the script (recursively)
- user defined commands defined in the script
Thus not in:
- other scripts sourced from this one
- mappings
- menus
- etc.

Script variables can be used to avoid conflicts with global variable names.
Take this example: 

        let s:counter = 0
        function MyCounter()
          let s:counter = s:counter + 1
          echo s:counter
        endfunction
        command Tick call MyCounter()

You can now invoke "Tick" from any script, and the "s:counter" variable in
that script will not be changed, only the "s:counter" in the script where
"Tick" was defined is used.

Another example that does the same: 

        let s:counter = 0
        command Tick let s:counter = s:counter + 1 | echo s:counter

When calling a function and invoking a user-defined command, the context for
script variables is set to the script where the function or command was
defined.

The script variables are also available when a function is defined inside a
function that is defined in a script.  Example: 

        let s:counter = 0
        function StartCounting(incr)
          if a:incr
            function MyCounter()
              let s:counter = s:counter + 1
            endfunction
          else
            function MyCounter()
              let s:counter = s:counter - 1
            endfunction
          endif
        endfunction

This defines the MyCounter() function either for counting up or counting down
when calling StartCounting().  It doesn't matter from where StartCounting() is
called, the s:counter variable will be accessible in MyCounter().

When the same script is sourced again it will use the same script variables.
They will remain valid as long as Vim is running.  This can be used to
maintain a counter: 

        if !exists("s:counter")
          let s:counter = 1
          echo "script executed for the first time"
        else
          let s:counter = s:counter + 1
          echo "script executed " .. s:counter .. " times now"
        endif

Note that this means that filetype plugins don't get a different set of script
variables for each buffer.  Use local buffer variables instead b:var.


PREDEFINED VIM VARIABLES                        vim-variable v:var v:
                                                        E963 E1063
Some variables can be set by the user, but the type cannot be changed.

                                        v:argv argv-variable
v:argv          The command line arguments Vim was invoked with.  This is a
                list of strings.  The first item is the Vim command.
                See v:progpath for the command with full path.

                                        v:beval_col beval_col-variable
v:beval_col     The number of the column, over which the mouse pointer is.
                This is the byte index in the v:beval_lnum line.
                Only valid while evaluating the 'balloonexpr' option.

                                        v:beval_bufnr beval_bufnr-variable
v:beval_bufnr   The number of the buffer, over which the mouse pointer is. Only
                valid while evaluating the 'balloonexpr' option.

                                        v:beval_lnum beval_lnum-variable
v:beval_lnum    The number of the line, over which the mouse pointer is. Only
                valid while evaluating the 'balloonexpr' option.

                                        v:beval_text beval_text-variable
v:beval_text    The text under or after the mouse pointer.  Usually a word as
                it is useful for debugging a C program.  'iskeyword' applies,
                but a dot and "->" before the position is included.  When on a
                ']' the text before it is used, including the matching '[' and
                word before it.  When on a Visual area within one line the
                highlighted text is used.  Also see <cexpr>.
                Only valid while evaluating the 'balloonexpr' option.

                                        v:beval_winnr beval_winnr-variable
v:beval_winnr   The number of the window, over which the mouse pointer is. Only
                valid while evaluating the 'balloonexpr' option.  The first
                window has number zero (unlike most other places where a
                window gets a number).

                                        v:beval_winid beval_winid-variable
v:beval_winid   The window-ID of the window, over which the mouse pointer
                is.  Otherwise like v:beval_winnr.

                                        v:char char-variable
v:char          Argument for evaluating 'formatexpr' and used for the typed
                character when using <expr> in an abbreviation :map-<expr>.
                It is also used by the InsertCharPre and InsertEnter events.

                        v:charconvert_from charconvert_from-variable
v:charconvert_from
                The name of the character encoding of a file to be converted.
                Only valid while evaluating the 'charconvert' option.

                        v:charconvert_to charconvert_to-variable
v:charconvert_to
                The name of the character encoding of a file after conversion.
                Only valid while evaluating the 'charconvert' option.

                                        v:cmdarg cmdarg-variable
v:cmdarg        This variable is used for two purposes:
                1. The extra arguments given to a file read/write command.
                   Currently these are "++enc=" and "++ff=".  This variable is
                   set before an autocommand event for a file read/write
                   command is triggered.  There is a leading space to make it
                   possible to append this variable directly after the
                   read/write command.  Note: The "+cmd" argument isn't
                   included here, because it will be executed anyway.
                2. When printing a PostScript file with ":hardcopy" this is
                   the argument for the ":hardcopy" command.  This can be used
                   in 'printexpr'.

                                        v:cmdbang cmdbang-variable
v:cmdbang       Set like v:cmdarg for a file read/write command.  When a "!"
                was used the value is 1, otherwise it is 0.  Note that this
                can only be used in autocommands.  For user commands <bang>
                can be used.
                                                v:collate collate-variable
v:collate       The current locale setting for collation order of the runtime
                environment.  This allows Vim scripts to be aware of the
                current locale encoding.  Technical: it's the value of
                LC_COLLATE.  When not using a locale the value is "C".
                This variable can not be set directly, use the :language
                command.
                See multi-lang.

                                                                v:colornames
v:colornames    A dictionary that maps color names to hex color strings. These
                color names can be used with the highlight-guifg,
                highlight-guibg, and highlight-guisp parameters. Updating
                an entry in v:colornames has no immediate effect on the syntax
                highlighting. The highlight commands (probably in a
                colorscheme script) need to be re-evaluated in order to use
                the updated color values. For example: 

                    :let v:colornames['fuscia'] = '#cf3ab4'
                    :let v:colornames['mauve'] = '#915f6d'
                    :highlight Normal guifg=fuscia guibg=mauve

                This cannot be used to override the cterm-colors but it can
                be used to override other colors. For example, the X11 colors
                defined in the colors/lists/default.vim (previously defined
                in rgb.txt). When defining new color names in a plugin, the
                recommended practice is to set a color entry only when it does
                not already exist. For example: 

                    :call extend(v:colornames, {
                        \ 'fuscia': '#cf3ab4',
                        \ 'mauve': '#915f6d,
                        \ }, 'keep')

                Using extend() with the 'keep' option updates each color only
                if it did not exist in v:colornames. Doing so allows the
                user to choose the precise color value for a common name
                by setting it in their .vimrc.

                It is possible to remove entries from this dictionary but
                doing so is NOT recommended, because it is disruptive to
                other scripts. It is also unlikely to achieve the desired
                result because the :colorscheme and :highlight commands will
                both automatically load all colors/lists/default.vim color
                scripts.

                                v:completed_item completed_item-variable
v:completed_item
                Dictionary containing the complete-items for the most
                recently completed word after CompleteDone.  The
                Dictionary is empty if the completion failed.

                                        v:count count-variable
v:count         The count given for the last Normal mode command.  Can be used
                to get the count before a mapping.  Read-only.  Example: 
        :map _x :<C-U>echo "the count is " .. v:count<CR>
               Note: The <C-U> is required to remove the line range that you
                get when typing ':' after a count.
                When there are two counts, as in "3d2w", they are multiplied,
                just like what happens in the command, "d6w" for the example.
                Also used for evaluating the 'formatexpr' option.
                "count" also works, for backwards compatibility, unless
                scriptversion is 3 or higher.

                                        v:count1 count1-variable
v:count1        Just like "v:count", but defaults to one when no count is
                used.

                                                v:ctype ctype-variable
v:ctype         The current locale setting for characters of the runtime
                environment.  This allows Vim scripts to be aware of the
                current locale encoding.  Technical: it's the value of
                LC_CTYPE.  When not using a locale the value is "C".
                This variable can not be set directly, use the :language
                command.
                See multi-lang.

                                        v:dying dying-variable
v:dying         Normally zero.  When a deadly signal is caught it's set to
                one.  When multiple signals are caught the number increases.
                Can be used in an autocommand to check if Vim didn't
                terminate normally. {only works on Unix}
                Example: 
        :au VimLeave * if v:dying | echo "\nAAAAaaaarrrggghhhh!!!\n" | endif
               Note: if another deadly signal is caught when v:dying is one,
                VimLeave autocommands will not be executed.

                                        v:exiting exiting-variable
v:exiting       Vim exit code.  Normally zero, non-zero when something went
                wrong.  The value is v:null before invoking the VimLeavePre
                and VimLeave autocmds.  See :q, :x and :cquit.
                Example: 
                        :au VimLeave * echo "Exit value is " .. v:exiting

                                        v:echospace echospace-variable
v:echospace     Number of screen cells that can be used for an :echo message
                in the last screen line before causing the hit-enter-prompt.
                Depends on 'showcmd', 'ruler' and 'columns'.  You need to
                check 'cmdheight' for whether there are full-width lines
                available above the last line.

                                        v:errmsg errmsg-variable
v:errmsg        Last given error message.  It's allowed to set this variable.
                Example: 
        :let v:errmsg = ""
        :silent! next
        :if v:errmsg != ""
        :  ... handle error
               "errmsg" also works, for backwards compatibility, unless
                scriptversion is 3 or higher.

                                v:errors errors-variable assert-return
v:errors        Errors found by assert functions, such as assert_true().
                This is a list of strings.
                The assert functions append an item when an assert fails.
                The return value indicates this: a one is returned if an item
                was added to v:errors, otherwise zero is returned.
                To remove old results make it empty: 
        :let v:errors = []
               If v:errors is set to anything but a list it is made an empty
                list by the assert function.

                                        v:event event-variable
v:event         Dictionary containing information about the current
                autocommand.  See the specific event for what it puts in
                this dictionary.
                The dictionary is emptied when the autocommand finishes,
                please refer to dict-identity for how to get an independent
                copy of it.  Use deepcopy() if you want to keep the
                information after the event triggers.  Example: 
                        au TextYankPost * let g:foo = deepcopy(v:event)

                                        v:exception exception-variable
v:exception     The value of the exception most recently caught and not
                finished.  See also v:throwpoint and throw-variables.
                Example: 
        :try
        :  throw "oops"
        :catch /.*/
        :  echo "caught " .. v:exception
        :endtry
               Output: "caught oops".

                                        v:false false-variable
v:false         A Number with value zero. Used to put "false" in JSON.  See
                json_encode().
                When used as a string this evaluates to "v:false". 
                        echo v:false
                       v:false 
                That is so that eval() can parse the string back to the same
                value.  Read-only.
                In Vim9 script "false" can be used which has a boolean type.

                                        v:fcs_reason fcs_reason-variable
v:fcs_reason    The reason why the FileChangedShell event was triggered.
                Can be used in an autocommand to decide what to do and/or what
                to set v:fcs_choice to.  Possible values:
                        deleted         file no longer exists
                        conflict        file contents, mode or timestamp was
                                        changed and buffer is modified
                        changed         file contents has changed
                        mode            mode of file changed
                        time            only file timestamp changed

                                        v:fcs_choice fcs_choice-variable
v:fcs_choice    What should happen after a FileChangedShell event was
                triggered.  Can be used in an autocommand to tell Vim what to
                do with the affected buffer:
                        reload          Reload the buffer (does not work if
                                        the file was deleted).
                        edit            Reload the buffer and detect the
                                        values for options such as
                                        'fileformat', 'fileencoding', 'binary'
                                        (does not work if the file was
                                        deleted).
                        ask             Ask the user what to do, as if there
                                        was no autocommand.  Except that when
                                        only the timestamp changed nothing
                                        will happen.
                        <empty>         Nothing, the autocommand should do
                                        everything that needs to be done.
                The default is empty.  If another (invalid) value is used then
                Vim behaves like it is empty, there is no warning message.

                                        v:fname fname-variable
v:fname         When evaluating 'includeexpr': the file name that was
                detected.  Empty otherwise.

                                        v:fname_in fname_in-variable
v:fname_in      The name of the input file.  Valid while evaluating:
                        option          used for 
                        'charconvert'   file to be converted
                        'diffexpr'      original file
                        'patchexpr'     original file
                        'printexpr'     file to be printed
                And set to the swap file name for SwapExists.

                                        v:fname_out fname_out-variable
v:fname_out     The name of the output file.  Only valid while
                evaluating:
                        option          used for 
                        'charconvert'   resulting converted file (*)
                        'diffexpr'      output of diff
                        'patchexpr'     resulting patched file
                (*) When doing conversion for a write command (e.g., ":w
                file") it will be equal to v:fname_in.  When doing conversion
                for a read command (e.g., ":e file") it will be a temporary
                file and different from v:fname_in.

                                        v:fname_new fname_new-variable
v:fname_new     The name of the new version of the file.  Only valid while
                evaluating 'diffexpr'.

                                        v:fname_diff fname_diff-variable
v:fname_diff    The name of the diff (patch) file.  Only valid while
                evaluating 'patchexpr'.

                                        v:folddashes folddashes-variable
v:folddashes    Used for 'foldtext': dashes representing foldlevel of a closed
                fold.
                Read-only in the sandbox. fold-foldtext

                                        v:foldlevel foldlevel-variable
v:foldlevel     Used for 'foldtext': foldlevel of closed fold.
                Read-only in the sandbox. fold-foldtext

                                        v:foldend foldend-variable
v:foldend       Used for 'foldtext': last line of closed fold.
                Read-only in the sandbox. fold-foldtext

                                        v:foldstart foldstart-variable
v:foldstart     Used for 'foldtext': first line of closed fold.
                Read-only in the sandbox. fold-foldtext

                                        v:hlsearch hlsearch-variable
v:hlsearch      Variable that indicates whether search highlighting is on.
                Setting it makes sense only if 'hlsearch' is enabled which
                requires +extra_search. Setting this variable to zero acts
                like the :nohlsearch command, setting it to one acts like 
                        let &hlsearch = &hlsearch
               Note that the value is restored when returning from a
                function. function-search-undo.

                                        v:insertmode insertmode-variable
v:insertmode    Used for the InsertEnter and InsertChange autocommand
                events.  Values:
                        i       Insert mode
                        r       Replace mode
                        v       Virtual Replace mode

                                                v:key key-variable
v:key           Key of the current item of a Dictionary.  Only valid while
                evaluating the expression used with map() and filter().
                Read-only.

                                                v:lang lang-variable
v:lang          The current locale setting for messages of the runtime
                environment.  This allows Vim scripts to be aware of the
                current language.  Technical: it's the value of LC_MESSAGES.
                The value is system dependent.
                This variable can not be set directly, use the :language
                command.
                It can be different from v:ctype when messages are desired
                in a different language than what is used for character
                encoding.  See multi-lang.

                                                v:lc_time lc_time-variable
v:lc_time       The current locale setting for time messages of the runtime
                environment.  This allows Vim scripts to be aware of the
                current language.  Technical: it's the value of LC_TIME.
                This variable can not be set directly, use the :language
                command.  See multi-lang.

                                                v:lnum lnum-variable
v:lnum          Line number for the 'foldexpr' fold-expr, 'formatexpr' and
                'indentexpr' expressions, tab page number for 'guitablabel'
                and 'guitabtooltip'.  Only valid while one of these
                expressions is being evaluated.  Read-only when in the
                sandbox.

                                                v:maxcol maxcol-variable
v:maxcol        Maximum line length.  Depending on where it is used it can be
                screen columns, characters or bytes.  The value currently is
                2147483647 on all systems.

                                        v:mouse_win mouse_win-variable
v:mouse_win     Window number for a mouse click obtained with getchar().
                First window has number 1, like with winnr().  The value is
                zero when there was no mouse button click.

                                        v:mouse_winid mouse_winid-variable
v:mouse_winid   Window ID for a mouse click obtained with getchar().
                The value is zero when there was no mouse button click.

                                        v:mouse_lnum mouse_lnum-variable
v:mouse_lnum    Line number for a mouse click obtained with getchar().
                This is the text line number, not the screen line number.  The
                value is zero when there was no mouse button click.

                                        v:mouse_col mouse_col-variable
v:mouse_col     Column number for a mouse click obtained with getchar().
                This is the screen column number, like with virtcol().  The
                value is zero when there was no mouse button click.

                                        v:none none-variable None
v:none          An empty String. Used to put an empty item in JSON.  See
                json_encode().
                This can also be used as a function argument to use the
                default value, see none-function_argument.
                When used as a number this evaluates to zero.
                When used as a string this evaluates to "v:none". 
                        echo v:none
                       v:none 
                That is so that eval() can parse the string back to the same
                value.  Read-only.
                Note that using `== v:none` and `!= v:none`  will often give
                an error.  Instead, use `is v:none` and `isnot v:none` .

                                        v:null null-variable
v:null          An empty String. Used to put "null" in JSON.  See
                json_encode().
                When used as a number this evaluates to zero.
                When used as a string this evaluates to "v:null". 
                        echo v:null
                       v:null 
                That is so that eval() can parse the string back to the same
                value.  Read-only.
                In Vim9 script null can be used without "v:".
                In some places v:null and null can be used for a List,
                Dict, Job, etc. that is not set.  That is slightly different
                than an empty List, Dict, etc.

                                        v:numbermax numbermax-variable
v:numbermax     Maximum value of a number.

                                        v:numbermin numbermin-variable
v:numbermin     Minimum value of a number (negative).

                                        v:numbersize numbersize-variable
v:numbersize    Number of bits in a Number.  This is normally 64, but on some
                systems it may be 32.

                                        v:oldfiles oldfiles-variable
v:oldfiles      List of file names that is loaded from the viminfo file on
                startup.  These are the files that Vim remembers marks for.
                The length of the List is limited by the ' argument of the
                'viminfo' option (default is 100).
                When the viminfo file is not used the List is empty.
                Also see :oldfiles and c_#<.
                The List can be modified, but this has no effect on what is
                stored in the viminfo file later.  If you use values other
                than String this will cause trouble.
                {only when compiled with the |+viminfo| feature}

                                                    v:option_new
v:option_new    New value of the option. Valid while executing an OptionSet
                autocommand.
                                                    v:option_old
v:option_old    Old value of the option. Valid while executing an OptionSet
                autocommand. Depending on the command used for setting and the
                kind of option this is either the local old value or the
                global old value.
                                                    v:option_oldlocal
v:option_oldlocal
                Old local value of the option. Valid while executing an
                OptionSet autocommand.
                                                    v:option_oldglobal
v:option_oldglobal
                Old global value of the option. Valid while executing an
                OptionSet autocommand.
                                                    v:option_type
v:option_type   Scope of the set command. Valid while executing an
                OptionSet autocommand. Can be either "global" or "local"
                                                    v:option_command
v:option_command
                Command used to set the option. Valid while executing an
                OptionSet autocommand.
                        value           option was set via   
                        "setlocal"      :setlocal or ":let l:xxx"
                        "setglobal"     :setglobal or ":let g:xxx"
                        "set"           :set or :let
                        "modeline"      modeline
                                        v:operator operator-variable
v:operator      The last operator given in Normal mode.  This is a single
                character except for commands starting with <g> or <z>,
                in which case it is two characters.  Best used alongside
                v:prevcount and v:register.  Useful if you want to cancel
                Operator-pending mode and then use the operator, e.g.: 
                        :omap O <Esc>:call MyMotion(v:operator)<CR>
               The value remains set until another operator is entered, thus
                don't expect it to be empty.
                v:operator is not set for :delete, :yank or other Ex
                commands.
                Read-only.

                                        v:prevcount prevcount-variable
v:prevcount     The count given for the last but one Normal mode command.
                This is the v:count value of the previous command.  Useful if
                you want to cancel Visual or Operator-pending mode and then
                use the count, e.g.: 
                        :vmap % <Esc>:call MyFilter(v:prevcount)<CR>
               Read-only.

                                        v:profiling profiling-variable
v:profiling     Normally zero.  Set to one after using ":profile start".
                See profiling.

                                        v:progname progname-variable
v:progname      Contains the name (with path removed) with which Vim was
                invoked.  Allows you to do special initialisations for view,
                evim etc., or any other name you might symlink to Vim.
                Read-only.

                                        v:progpath progpath-variable
v:progpath      Contains the command with which Vim was invoked, in a form
                that when passed to the shell will run the same Vim executable
                as the current one (if $PATH remains unchanged).
                Useful if you want to message a Vim server using a
                --remote-expr.
                To get the full path use: 
                        echo exepath(v:progpath)
               If the command has a relative path it will be expanded to the
                full path, so that it still works after :cd. Thus starting
                "./vim" results in "/home/user/path/to/vim/src/vim".
                On Linux and other systems it will always be the full path.
                On Mac it may just be "vim" and using exepath() as mentioned
                above should be used to get the full path.
                On MS-Windows the executable may be called "vim.exe", but the
                ".exe" is not added to v:progpath.
                Read-only.

                                        v:register register-variable
v:register      The name of the register in effect for the current normal mode
                command (regardless of whether that command actually used a
                register).  Or for the currently executing normal mode mapping
                (use this in custom commands that take a register).
                If none is supplied it is the default register '"', unless
                'clipboard' contains "unnamed" or "unnamedplus", then it is
                '*' or '+'.
                Also see getreg() and setreg()

                                        v:scrollstart scrollstart-variable
v:scrollstart   String describing the script or function that caused the
                screen to scroll up.  It's only set when it is empty, thus the
                first reason is remembered.  It is set to "Unknown" for a
                typed command.
                This can be used to find out why your script causes the
                hit-enter prompt.

                                        v:servername servername-variable
v:servername    The resulting registered client-server-name if any.
                Read-only.


v:searchforward                 v:searchforward searchforward-variable
                Search direction:  1 after a forward search, 0 after a
                backward search.  It is reset to forward when directly setting
                the last search pattern, see quote/.
                Note that the value is restored when returning from a
                function. function-search-undo.
                Read-write.

                                        v:shell_error shell_error-variable
v:shell_error   Result of the last shell command.  When non-zero, the last
                shell command had an error.  When zero, there was no problem.
                This only works when the shell returns the error code to Vim.
                The value -1 is often used when the command could not be
                executed.  Read-only.
                Example: 
        :!mv foo bar
        :if v:shell_error
        :  echo 'could not rename "foo" to "bar"!'
        :endif
               "shell_error" also works, for backwards compatibility, unless
                scriptversion is 3 or higher.

                                        v:sizeofint sizeofint-variable
v:sizeofint     Number of bytes in an int.  Depends on how Vim was compiled.
                This is only useful for deciding whether a test will give the
                expected result.

                                        v:sizeoflong sizeoflong-variable
v:sizeoflong    Number of bytes in a long.  Depends on how Vim was compiled.
                This is only useful for deciding whether a test will give the
                expected result.

                                v:sizeofpointer sizeofpointer-variable
v:sizeofpointer Number of bytes in a pointer.  Depends on how Vim was compiled.
                This is only useful for deciding whether a test will give the
                expected result.

                                        v:statusmsg statusmsg-variable
v:statusmsg     Last given status message.  It's allowed to set this variable.

                                        v:swapname swapname-variable
v:swapname      Only valid when executing SwapExists autocommands: Name of
                the swap file found.  Read-only.

                                        v:swapchoice swapchoice-variable
v:swapchoice    SwapExists autocommands can set this to the selected choice
                for handling an existing swap file:
                        'o'     Open read-only
                        'e'     Edit anyway
                        'r'     Recover
                        'd'     Delete swapfile
                        'q'     Quit
                        'a'     Abort
                The value should be a single-character string.  An empty value
                results in the user being asked, as would happen when there is
                no SwapExists autocommand.  The default is empty.

                                        v:swapcommand swapcommand-variable
v:swapcommand   Normal mode command to be executed after a file has been
                opened.  Can be used for a SwapExists autocommand to have
                another Vim open the file and jump to the right place.  For
                example, when jumping to a tag the value is ":tag tagname\r".
                For ":edit +cmd file" the value is ":cmd\r".

                                v:t_TYPE v:t_bool t_bool-variable
v:t_bool        Value of Boolean type.  Read-only.  See: type()
                                        v:t_channel t_channel-variable
v:t_channel     Value of Channel type.  Read-only.  See: type()
                                        v:t_dict t_dict-variable
v:t_dict        Value of Dictionary type.  Read-only.  See: type()
                                        v:t_float t_float-variable
v:t_float       Value of Float type.  Read-only.  See: type()
                                        v:t_func t_func-variable
v:t_func        Value of Funcref type.  Read-only.  See: type()
                                        v:t_job t_job-variable
v:t_job         Value of Job type.  Read-only.  See: type()
                                        v:t_list t_list-variable
v:t_list        Value of List type.  Read-only.  See: type()
                                        v:t_none t_none-variable
v:t_none        Value of None type.  Read-only.  See: type()
                                        v:t_number t_number-variable
v:t_number      Value of Number type.  Read-only.  See: type()
                                        v:t_string t_string-variable
v:t_string      Value of String type.  Read-only.  See: type()
                                        v:t_blob t_blob-variable
v:t_blob        Value of Blob type.  Read-only.  See: type()

                                v:termresponse termresponse-variable
v:termresponse  The escape sequence returned by the terminal for the t_RV
                termcap entry.  It is set when Vim receives an escape sequence
                that starts with ESC [ or CSI, then '>' or '?' and ends in a
                'c', with only digits and ';' in between.
                When this option is set, the TermResponse autocommand event is
                fired, so that you can react to the response from the
                terminal.  You can use terminalprops() to see what Vim
                figured out about the terminal.
                The response from a new xterm is: "<Esc>[> Pp ; Pv ; Pc c".  Pp
                is the terminal type: 0 for vt100 and 1 for vt220.  Pv is the
                patch level (since this was introduced in patch 95, it's
                always 95 or higher).  Pc is always zero.
                If Pv is 141 or higher then Vim will try to request terminal
                codes.  This only works with xterm xterm-codes.
                {only when compiled with |+termresponse| feature}

                                                v:termblinkresp
v:termblinkresp The escape sequence returned by the terminal for the t_RC
                termcap entry.  This is used to find out whether the terminal
                cursor is blinking. This is used by term_getcursor().

                                                v:termstyleresp
v:termstyleresp The escape sequence returned by the terminal for the t_RS
                termcap entry.  This is used to find out what the shape of the
                cursor is.  This is used by term_getcursor().

                                                v:termrbgresp
v:termrbgresp   The escape sequence returned by the terminal for the t_RB
                termcap entry.  This is used to find out what the terminal
                background color is, see 'background'.

                                                v:termrfgresp
v:termrfgresp   The escape sequence returned by the terminal for the t_RF
                termcap entry.  This is used to find out what the terminal
                foreground color is.

                                                v:termu7resp
v:termu7resp    The escape sequence returned by the terminal for the t_u7
                termcap entry.  This is used to find out what the terminal
                does with ambiguous width characters, see 'ambiwidth'.

                                        v:testing testing-variable
v:testing       Must be set before using test_garbagecollect_now().
                Also, when set certain error messages won't be shown for 2
                seconds. (e.g. "'dictionary' option is empty")

                                v:this_session this_session-variable
v:this_session  Full filename of the last loaded or saved session file.  See
                :mksession.  It is allowed to set this variable.  When no
                session file has been saved, this variable is empty.
                "this_session" also works, for backwards compatibility, unless
                scriptversion is 3 or higher

                                        v:throwpoint throwpoint-variable
v:throwpoint    The point where the exception most recently caught and not
                finished was thrown.  Not set when commands are typed.  See
                also v:exception and throw-variables.
                Example: 
        :try
        :  throw "oops"
        :catch /.*/
        :  echo "Exception from" v:throwpoint
        :endtry
               Output: "Exception from test.vim, line 2"

                                                v:true true-variable
v:true          A Number with value one. Used to put "true" in JSON.  See
                json_encode().
                When used as a string this evaluates to "v:true". 
                        echo v:true
                       v:true 
                That is so that eval() can parse the string back to the same
                value.  Read-only.
                In Vim9 script "true" can be used which has a boolean type.
                                                v:val val-variable
v:val           Value of the current item of a List or Dictionary.  Only
                valid while evaluating the expression used with map() and
                filter().  Read-only.

                                        v:version version-variable
v:version       Version number of Vim: Major version number times 100 plus
                minor version number.  Version 5.0 is 500.  Version 5.1
                is 501.  Read-only.  "version" also works, for backwards
                compatibility, unless scriptversion is 3 or higher.
                Use has() to check if a certain patch was included, e.g.: 
                        if has("patch-7.4.123")
               Note that patch numbers are specific to the version, thus both
                version 5.0 and 5.1 may have a patch 123, but these are
                completely different.

                                        v:versionlong versionlong-variable
v:versionlong   Like v:version, but also including the patchlevel in the last
                four digits.  Version 8.1 with patch 123 has value 8010123.
                This can be used like this: 
                        if v:versionlong >= 8010123
               However, if there are gaps in the list of patches included
                this will not work well.  This can happen if a recent patch
                was included into an older version, e.g. for a security fix.
                Use the has() function to make sure the patch is actually
                included.

                                v:vim_did_enter vim_did_enter-variable
v:vim_did_enter Zero until most of startup is done.  It is set to one just
                before VimEnter autocommands are triggered.

                                        v:warningmsg warningmsg-variable
v:warningmsg    Last given warning message.  It's allowed to set this variable.

                                        v:windowid windowid-variable
v:windowid      When any X11 based GUI is running or when running in a
                terminal and Vim connects to the X server (-X) this will be
                set to the window ID.
                When an MS-Windows GUI is running this will be set to the
                window handle.
                Otherwise the value is zero.
                Note: for windows inside Vim use winnr() or win_getid(),
                see window-ID.

==============================================================================
4. Builtin Functions                                    functions

See function-list for a list grouped by what the function is used for.

The alphabetic list of all builtin functions and details are in a separate
help file: builtin-functions.

==============================================================================
5. Defining functions                                   user-functions

New functions can be defined.  These can be called just like builtin
functions.  The function executes a sequence of Ex commands.  Normal mode
commands can be executed with the :normal command.

This section is about the legacy functions. For the Vim9 functions, which
execute much faster, support type checking and more, see vim9.txt.

The function name must start with an uppercase letter, to avoid confusion with
builtin functions.  To prevent from using the same name in different scripts
avoid obvious, short names.  A good habit is to start the function name with
the name of the script, e.g., "HTMLcolor()".

In legacy script it is also possible to use curly braces, see
curly-braces-names.
The autoload facility is useful to define a function only when it's called.

                                                        local-function
A function local to a legacy script must start with "s:".  A local script
function can only be called from within the script and from functions, user
commands and autocommands defined in the script.  It is also possible to call
the function from a mapping defined in the script, but then <SID> must be
used instead of "s:" when the mapping is expanded outside of the script.
There are only script-local functions, no buffer-local or window-local
functions.

In Vim9 script functions are local to the script by default, prefix "g:" to
define a global function.

                                :fu :function E128 E129 E123 E454
:fu[nction]             List all functions and their arguments.

:fu[nction] {name}      List function {name}.
                        {name} can also be a Dictionary entry that is a
                        Funcref: 
                                :function dict.init

:fu[nction] /{pattern}  List functions with a name matching {pattern}.
                        Example that lists all functions ending with "File": 
                                :function /File$

                                                        :function-verbose
When 'verbose' is non-zero, listing a function will also display where it was
last defined. Example: 

    :verbose function SetFileTypeSH
        function SetFileTypeSH(name)
            Last set from /usr/share/vim/vim-7.0/filetype.vim

See :verbose-cmd for more information.

                                                E124 E125 E853 E884
:fu[nction][!] {name}([arguments]) [range] [abort] [dict] [closure]
                        Define a new function by the name {name}.  The body of
                        the function follows in the next lines, until the
                        matching :endfunction.

                        The name must be made of alphanumeric characters and
                        '_', and must start with a capital or "s:" (see
                        above).  Note that using "b:" or "g:" is not allowed.
                        (since patch 7.4.260 E884 is given if the function
                        name has a colon in the name, e.g. for "foo:bar()".
                        Before that patch no error was given).

                        {name} can also be a Dictionary entry that is a
                        Funcref: 
                                :function dict.init(arg)
                       "dict" must be an existing dictionary.  The entry
                        "init" is added if it didn't exist yet.  Otherwise [!]
                        is required to overwrite an existing function.  The
                        result is a Funcref to a numbered function.  The
                        function can only be used with a Funcref and will be
                        deleted if there are no more references to it.
                                                                E127 E122
                        When a function by this name already exists and [!] is
                        not used an error message is given.  There is one
                        exception: When sourcing a script again, a function
                        that was previously defined in that script will be
                        silently replaced.
                        When [!] is used, an existing function is silently
                        replaced.  Unless it is currently being executed, that
                        is an error.
                        NOTE: Use ! wisely.  If used without care it can cause
                        an existing function to be replaced unexpectedly,
                        which is hard to debug.
                        NOTE: In Vim9 script script-local functions cannot be
                        deleted or redefined.

                        For the {arguments} see function-argument.

                                        :func-range a:firstline a:lastline
                        When the [range] argument is added, the function is
                        expected to take care of a range itself.  The range is
                        passed as "a:firstline" and "a:lastline".  If [range]
                        is excluded, ":{range}call" will call the function for
                        each line in the range, with the cursor on the start
                        of each line.  See function-range-example.
                        The cursor is still moved to the first line of the
                        range, as is the case with all Ex commands.
                                                                :func-abort
                        When the [abort] argument is added, the function will
                        abort as soon as an error is detected.
                                                                :func-dict
                        When the [dict] argument is added, the function must
                        be invoked through an entry in a Dictionary.  The
                        local variable "self" will then be set to the
                        dictionary.  See Dictionary-function.
                                                :func-closure E932
                        When the [closure] argument is added, the function
                        can access variables and arguments from the outer
                        scope.  This is usually called a closure.  In this
                        example Bar() uses "x" from the scope of Foo().  It
                        remains referenced even after Foo() returns: 
                                :function! Foo()
                                :  let x = 0
                                :  function! Bar() closure
                                :    let x += 1
                                :    return x
                                :  endfunction
                                :  return funcref('Bar')
                                :endfunction

                                :let F = Foo()
                                :echo F()
                               1 
                                :echo F()
                               2 
                                :echo F()
                               3

                                                function-search-undo
                        The last used search pattern and the redo command "."
                        will not be changed by the function.  This also
                        implies that the effect of :nohlsearch is undone
                        when the function returns.

                        :endf :endfunction E126 E193 W22 E1151
:endf[unction] [argument]
                        The end of a function definition.  Best is to put it
                        on a line by its own, without [argument].

                        [argument] can be:
                                | command       command to execute next
                                \n command      command to execute next
                                " comment       always ignored
                                anything else   ignored, warning given when
                                                'verbose' is non-zero
                        The support for a following command was added in Vim
                        8.0.0654, before that any argument was silently
                        ignored.

                        To be able to define a function inside an :execute
                        command, use line breaks instead of :bar: 
                                :exe "func Foo()\necho 'foo'\nendfunc"

                                :delf :delfunction E131 E933 E1084
:delf[unction][!] {name}
                        Delete function {name}.
                        {name} can also be a Dictionary entry that is a
                        Funcref: 
                                :delfunc dict.init
                       This will remove the "init" entry from "dict".  The
                        function is deleted if there are no more references to
                        it.
                        With the ! there is no error if the function does not
                        exist.
                                                        :retu :return E133
:retu[rn] [expr]        Return from a function.  When "[expr]" is given, it is
                        evaluated and returned as the result of the function.
                        If "[expr]" is not given, the number 0 is returned.
                        When a function ends without an explicit ":return",
                        the number 0 is returned.
                        In a :def function E1095 is given if unreachable
                        code follows after the :return.
                        In legacy script there is no check for unreachable
                        lines, thus there is no warning if commands follow
                        :return.

                        If the ":return" is used after a :try but before the
                        matching :finally (if present), the commands
                        following the ":finally" up to the matching :endtry
                        are executed first.  This process applies to all
                        nested ":try"s inside the function.  The function
                        returns at the outermost ":endtry".

                                                function-argument a:var
An argument can be defined by giving its name.  In the function this can then
be used as "a:name" ("a:" for argument).
                                        a:0 a:1 a:000 E740 ...
Up to 20 arguments can be given, separated by commas.  After the named
arguments an argument "..." can be specified, which means that more arguments
may optionally be following.  In the function the extra arguments can be used
as "a:1", "a:2", etc.  "a:0" is set to the number of extra arguments (which
can be 0).  "a:000" is set to a List that contains these arguments.  Note
that "a:1" is the same as "a:000[0]".
                                                        E742 E1090
The a: scope and the variables in it cannot be changed, they are fixed.
However, if a composite type is used, such as List or Dictionary , you can
change their contents.  Thus you can pass a List to a function and have the
function add an item to it.  If you want to make sure the function cannot
change a List or Dictionary use :lockvar.

It is also possible to define a function without any arguments.  You must
still supply the () then.

It is allowed to define another function inside a function body.

                                                optional-function-argument
You can provide default values for positional named arguments.  This makes
them optional for function calls.  When a positional argument is not
specified at a call, the default expression is used to initialize it.
This only works for functions declared with :function or :def, not for
lambda expressions expr-lambda.

Example: 
  function Something(key, value = 10)
     echo a:key .. ": " .. a:value
  endfunction
  call Something('empty')       "empty: 10"
  call Something('key', 20)     "key: 20"

The argument default expressions are evaluated at the time of the function
call, not definition.  Thus it is possible to use an expression which is
invalid the moment the function is defined.  The expressions are also only
evaluated when arguments are not specified during a call.
                                                none-function_argument
You can pass v:none to use the default expression.  Note that this means you
cannot pass v:none as an ordinary value when an argument has a default
expression.

Example: 
  function Something(a = 10, b = 20, c = 30)
  endfunction
  call Something(1, v:none, 3)      " b = 20

                                                                E989
Optional arguments with default expressions must occur after any mandatory
arguments.  You can use "..." after all optional named arguments.

It is possible for later argument defaults to refer to prior arguments,
but not the other way around.  They must be prefixed with "a:", as with all
arguments.

Example that works: 
  :function Okay(mandatory, optional = a:mandatory)
  :endfunction
Example that does NOT work: 
  :function NoGood(first = a:second, second = 10)
  :endfunction

When not using "...", the number of arguments in a function call must be at
least equal to the number of mandatory named arguments.  When using "...", the
number of arguments may be larger than the total of mandatory and optional
arguments.

                                                        local-variables
Inside a function local variables can be used.  These will disappear when the
function returns.  Global variables need to be accessed with "g:".

Example: 
  :function Table(title, ...)
  :  echohl Title
  :  echo a:title
  :  echohl None
  :  echo a:0 .. " items:"
  :  for s in a:000
  :    echon ' ' .. s
  :  endfor
  :endfunction

This function can then be called with: 
  call Table("Table", "line1", "line2")
  call Table("Empty Table")

To return more than one value, return a List: 
  :function Compute(n1, n2)
  :  if a:n2 == 0
  :    return ["fail", 0]
  :  endif
  :  return ["ok", a:n1 / a:n2]
  :endfunction

This function can then be called with: 
  :let [success, div] = Compute(102, 6)
  :if success == "ok"
  :  echo div
  :endif

                                                :cal :call E107
:[range]cal[l] {name}([arguments])
                Call a function.  The name of the function and its arguments
                are as specified with :function.  Up to 20 arguments can be
                used.  The returned value is discarded.
                In Vim9 script using :call is optional, these two lines do
                the same thing: 
                        call SomeFunc(arg)
                        SomeFunc(arg)
               Without a range and for functions that accept a range, the
                function is called once.  When a range is given the cursor is
                positioned at the start of the first line before executing the
                function.
                When a range is given and the function doesn't handle it
                itself, the function is executed for each line in the range,
                with the cursor in the first column of that line.  The cursor
                is left at the last line (possibly moved by the last function
                call).  The arguments are re-evaluated for each line.  Thus
                this works:
                                                function-range-example  
        :function Mynumber(arg)
        :  echo line(".") .. " " .. a:arg
        :endfunction
        :1,5call Mynumber(getline("."))

                The "a:firstline" and "a:lastline" are defined anyway, they
                can be used to do something different at the start or end of
                the range.

                Example of a function that handles the range itself: 

        :function Cont() range
        :  execute (a:firstline + 1) .. "," .. a:lastline .. 's/^/\t\\ '
        :endfunction
        :4,8call Cont()

                This function inserts the continuation character "\" in front
                of all the lines in the range, except the first one.

                When the function returns a composite value it can be further
                dereferenced, but the range will not be used then.  Example: 
        :4,8call GetDict().method()
               Here GetDict() gets the range but method() does not.

                                                                E117
When a function cannot be found the error "E117: Unknown function" will be
given.  If the function was using an autoload path or an autoload import and
the script is a Vim9 script, this may also be caused by the function not
being exported.

                                                                E132
The recursiveness of user functions is restricted with the 'maxfuncdepth'
option.

It is also possible to use :eval.  It does not support a range, but does
allow for method chaining, e.g.: 
        eval GetList()->Filter()->append('$')

A function can also be called as part of evaluating an expression or when it
is used as a method: 
        let x = GetList()
        let y = GetList()->Filter()


AUTOMATICALLY LOADING FUNCTIONS 
                                                        autoload-functions
When using many or large functions, it's possible to automatically define them
only when they are used.  There are two methods: with an autocommand and with
the "autoload" directory in 'runtimepath'.


Using an autocommand 

This is introduced in the user manual, section 51.4.

The autocommand is useful if you have a plugin that is a long Vim script file.
You can define the autocommand and quickly quit the script with :finish.
That makes Vim startup faster.  The autocommand should then load the same file
again, setting a variable to skip the :finish command.

Use the FuncUndefined autocommand event with a pattern that matches the
function(s) to be defined.  Example: 

        :au FuncUndefined BufNet* source ~/vim/bufnetfuncs.vim

The file "~/vim/bufnetfuncs.vim" should then define functions that start with
"BufNet".  Also see FuncUndefined.


Using an autoload script 
                                                        autoload E746
This is introduced in the user manual, section 51.5.

Using a script in the "autoload" directory is simpler, but requires using
exactly the right file name.  A function that can be autoloaded has a name
like this: 

        :call filename#funcname()

These functions are always global, in Vim9 script "g:" needs to be used: 
        :call g:filename#funcname()

When such a function is called, and it is not defined yet, Vim will search the
"autoload" directories in 'runtimepath' for a script file called
"filename.vim".  For example "~/.vim/autoload/filename.vim".  That file should
then define the function like this: 

        function filename#funcname()
           echo "Done!"
        endfunction

The file name and the name used before the # in the function must match
exactly, and the defined function must have the name exactly as it will be
called.  In Vim9 script the "g:" prefix must be used: 
        function g:filename#funcname()

or for a compiled function: 
        def g:filename#funcname()

It is possible to use subdirectories.  Every # in the function name works like
a path separator.  Thus when calling a function: 

        :call foo#bar#func()

Vim will look for the file "autoload/foo/bar.vim" in 'runtimepath'.

This also works when reading a variable that has not been set yet: 

        :let l = foo#bar#lvar

However, when the autoload script was already loaded it won't be loaded again
for an unknown variable.

When assigning a value to such a variable nothing special happens.  This can
be used to pass settings to the autoload script before it's loaded: 

        :let foo#bar#toggle = 1
        :call foo#bar#func()

Note that when you make a mistake and call a function that is supposed to be
defined in an autoload script, but the script doesn't actually define the
function, you will get an error message for the missing function.  If you fix
the autoload script it won't be automatically loaded again.  Either restart
Vim or manually source the script.

Also note that if you have two script files, and one calls a function in the
other and vice versa, before the used function is defined, it won't work.
Avoid using the autoload functionality at the toplevel.

In Vim9 script you will get error E1263 if you define a function with
a "#" character in the name.  You should use a name without "#" and use
:export.

Hint: If you distribute a bunch of scripts you can pack them together with the
vimball utility.  Also read the user manual distribute-script.

==============================================================================
6. Curly braces names                                   curly-braces-names

In most places where you can use a variable, you can use a "curly braces name"
variable.  This is a regular variable name with one or more expressions
wrapped in braces {} like this: 
        my_{adjective}_variable

This only works in legacy Vim script, not in Vim9 script.

When Vim encounters this, it evaluates the expression inside the braces, puts
that in place of the expression, and re-interprets the whole as a variable
name.  So in the above example, if the variable "adjective" was set to
"noisy", then the reference would be to "my_noisy_variable", whereas if
"adjective" was set to "quiet", then it would be to "my_quiet_variable".

One application for this is to create a set of variables governed by an option
value.  For example, the statement 
        echo my_{&background}_message

would output the contents of "my_dark_message" or "my_light_message" depending
on the current value of 'background'.

You can use multiple brace pairs: 
        echo my_{adverb}_{adjective}_message
..or even nest them: 
        echo my_{ad{end_of_word}}_message
where "end_of_word" is either "verb" or "jective".

However, the expression inside the braces must evaluate to a valid single
variable name, e.g. this is invalid: 
        :let foo='a + b'
        :echo c{foo}d
.. since the result of expansion is "ca + bd", which is not a variable name.

                                                curly-braces-function-names
You can call and define functions by an evaluated name in a similar way.
Example: 
        :let func_end='whizz'
        :call my_func_{func_end}(parameter)

This would call the function "my_func_whizz(parameter)".

This does NOT work: 
  :let i = 3
  :let @{i} = ''  " error
  :echo @{i}      " error

==============================================================================
7. Commands                                             expression-commands

Note: in Vim9 script :let is not used.  :var is used for variable
declarations and assignments do not use a command.  vim9-declaration

:let {var-name} = {expr1}                               :let E18
                        Set internal variable {var-name} to the result of the
                        expression {expr1}.  The variable will get the type
                        from the {expr}.  If {var-name} didn't exist yet, it
                        is created.

:let {var-name}[{idx}] = {expr1}                        E689 E1141
                        Set a list item to the result of the expression
                        {expr1}.  {var-name} must refer to a list and {idx}
                        must be a valid index in that list.  For nested list
                        the index can be repeated.
                        This cannot be used to add an item to a List.
                        This cannot be used to set a byte in a String.  You
                        can do that like this: 
                                :let var = var[0:2] .. 'X' .. var[4:]
                       When {var-name} is a Blob then {idx} can be the
                        length of the blob, in which case one byte is
                        appended.

                                        E711 E719 E1165 E1166 E1183
:let {var-name}[{idx1}:{idx2}] = {expr1}                E708 E709 E710
                        Set a sequence of items in a List to the result of
                        the expression {expr1}, which must be a list with the
                        correct number of items.
                        {idx1} can be omitted, zero is used instead.
                        {idx2} can be omitted, meaning the end of the list.
                        When the selected range of items is partly past the
                        end of the list, items will be added.

                        :let+= :let-= :letstar= :let/=  :let%=
                        :let.= :let..= E734 E985 E1019
:let {var} += {expr1}   Like ":let {var} = {var} + {expr1}".
:let {var} -= {expr1}   Like ":let {var} = {var} - {expr1}".
:let {var} *= {expr1}   Like ":let {var} = {var} * {expr1}".
:let {var} /= {expr1}   Like ":let {var} = {var} / {expr1}".
:let {var} %= {expr1}   Like ":let {var} = {var} % {expr1}".
:let {var} .= {expr1}   Like ":let {var} = {var} . {expr1}".
:let {var} ..= {expr1}  Like ":let {var} = {var} .. {expr1}".
                        These fail if {var} was not set yet and when the type
                        of {var} and {expr1} don't fit the operator.
                        .= is not supported with Vim script version 2 and
                        later, see vimscript-version.


:let ${env-name} = {expr1}                      :let-environment :let-$
                        Set environment variable {env-name} to the result of
                        the expression {expr1}.  The type is always String.

                        On some systems making an environment variable empty
                        causes it to be deleted.  Many systems do not make a
                        difference between an environment variable that is not
                        set and an environment variable that is empty.

:let ${env-name} .= {expr1}
                        Append {expr1} to the environment variable {env-name}.
                        If the environment variable didn't exist yet this
                        works like "=".

:let @{reg-name} = {expr1}                      :let-register :let-@
                        Write the result of the expression {expr1} in register
                        {reg-name}.  {reg-name} must be a single letter, and
                        must be the name of a writable register (see
                        registers).  "@@" can be used for the unnamed
                        register, "@/" for the search pattern.
                        If the result of {expr1} ends in a <CR> or <NL>, the
                        register will be linewise, otherwise it will be set to
                        characterwise.
                        This can be used to clear the last search pattern: 
                                :let @/ = ""
                       This is different from searching for an empty string,
                        that would match everywhere.

:let @{reg-name} .= {expr1}
                        Append {expr1} to register {reg-name}.  If the
                        register was empty it's like setting it to {expr1}.

:let &{option-name} = {expr1}                   :let-option :let-&
                        Set option {option-name} to the result of the
                        expression {expr1}.  A String or Number value is
                        always converted to the type of the option.
                        For an option local to a window or buffer the effect
                        is just like using the :set command: both the local
                        value and the global value are changed.
                        Example: 
                                :let &path = &path .. ',/usr/local/include'
                       This also works for terminal codes in the form t_xx.
                        But only for alphanumerical names.  Example: 
                                :let &t_k1 = "\<Esc>[234;"
                       When the code does not exist yet it will be created as
                        a terminal key code, there is no error.

:let &{option-name} .= {expr1}
                        For a string option: Append {expr1} to the value.
                        Does not insert a comma like :set+=.

:let &{option-name} += {expr1}
:let &{option-name} -= {expr1}
                        For a number or boolean option: Add or subtract
                        {expr1}.

:let &l:{option-name} = {expr1}
:let &l:{option-name} .= {expr1}
:let &l:{option-name} += {expr1}
:let &l:{option-name} -= {expr1}
                        Like above, but only set the local value of an option
                        (if there is one).  Works like :setlocal.

:let &g:{option-name} = {expr1}
:let &g:{option-name} .= {expr1}
:let &g:{option-name} += {expr1}
:let &g:{option-name} -= {expr1}
                        Like above, but only set the global value of an option
                        (if there is one).  Works like :setglobal.
                                                                E1093
:let [{name1}, {name2}, ...] = {expr1}          :let-unpack E687 E688
                        {expr1} must evaluate to a List.  The first item in
                        the list is assigned to {name1}, the second item to
                        {name2}, etc.
                        The number of names must match the number of items in
                        the List.
                        Each name can be one of the items of the ":let"
                        command as mentioned above.
                        Example: 
                                :let [s, item] = GetItem(s)
                       Detail: {expr1} is evaluated first, then the
                        assignments are done in sequence.  This matters if
                        {name2} depends on {name1}.  Example: 
                                :let x = [0, 1]
                                :let i = 0
                                :let [i, x[i]] = [1, 2]
                                :echo x
                       The result is [0, 2].

:let [{name1}, {name2}, ...] .= {expr1}
:let [{name1}, {name2}, ...] += {expr1}
:let [{name1}, {name2}, ...] -= {expr1}
                        Like above, but append/add/subtract the value for each
                        List item.

:let [{name}, ..., ; {lastname}] = {expr1}                              E452
                        Like :let-unpack above, but the List may have more
                        items than there are names.  A list of the remaining
                        items is assigned to {lastname}.  If there are no
                        remaining items {lastname} is set to an empty list.
                        Example: 
                                :let [a, b; rest] = ["aval", "bval", 3, 4]

:let [{name}, ..., ; {lastname}] .= {expr1}
:let [{name}, ..., ; {lastname}] += {expr1}
:let [{name}, ..., ; {lastname}] -= {expr1}
                        Like above, but append/add/subtract the value for each
                        List item.

                                                :let=<< :let-heredoc
                                        E990 E991 E172 E221 E1145
:let {var-name} =<< [trim] [eval] {endmarker}
text...
text...
{endmarker}
                        Set internal variable {var-name} to a List
                        containing the lines of text bounded by the string
                        {endmarker}.

                        If "eval" is not specified, then each line of text is
                        used as a literal-string, except that single quotes
                        doe not need to be doubled.
                        If "eval" is specified, then any Vim expression in the
                        form {expr} is evaluated and the result replaces the
                        expression, like with interp-string.
                        Example where $HOME is expanded: 
                                let lines =<< trim eval END
                                  some text
                                  See the file {$HOME}/.vimrc
                                  more text
                                END
                       There can be multiple Vim expressions in a single line
                        but an expression cannot span multiple lines.  If any
                        expression evaluation fails, then the assignment fails.

                        {endmarker} must not contain white space.
                        {endmarker} cannot start with a lower case character.
                        The last line should end only with the {endmarker}
                        string without any other character.  Watch out for
                        white space after {endmarker}!

                        Without "trim" any white space characters in the lines
                        of text are preserved.  If "trim" is specified before
                        {endmarker}, then indentation is stripped so you can
                        do: 
                                let text =<< trim END
                                   if ok
                                     echo 'done'
                                   endif
                                END
                       Results in: ["if ok", "  echo 'done'", "endif"]
                        The marker must line up with "let" and the indentation
                        of the first line is removed from all the text lines.
                        Specifically: all the leading indentation exactly
                        matching the leading indentation of the first
                        non-empty text line is stripped from the input lines.
                        All leading indentation exactly matching the leading
                        indentation before let is stripped from the line
                        containing {endmarker}.  Note that the difference
                        between space and tab matters here.

                        If {var-name} didn't exist yet, it is created.
                        Cannot be followed by another command, but can be
                        followed by a comment.

                        To avoid line continuation to be applied, consider
                        adding 'C' to 'cpoptions': 
                                set cpo+=C
                                let var =<< END
                                   \ leading backslash
                                END
                                set cpo-=C

                        Examples: 
                                let var1 =<< END
                                Sample text 1
                                    Sample text 2
                                Sample text 3
                                END

                                let data =<< trim DATA
                                        1 2 3 4
                                        5 6 7 8
                                DATA

                                let code =<< trim eval CODE
                                   let v = {10 + 20}
                                   let h = "{$HOME}"
                                   let s = "{Str1()} abc {Str2()}"
                                   let n = {MyFunc(3, 4)}
                                CODE

                                                                E121
:let {var-name} ..      List the value of variable {var-name}.  Multiple
                        variable names may be given.  Special names recognized
                        here:                           E738
                          g:    global variables
                          b:    local buffer variables
                          w:    local window variables
                          t:    local tab page variables
                          s:    script-local variables
                          l:    local function variables
                          v:    Vim variables.
                        This does not work in Vim9 script. vim9-declaration

:let                    List the values of all variables.  The type of the
                        variable is indicated before the value:
                            <nothing>   String
                                #       Number
                                *       Funcref
                        This does not work in Vim9 script. vim9-declaration

:unl[et][!] {name} ...                  :unlet :unl E108 E795 E1081
                        Remove the internal variable {name}.  Several variable
                        names can be given, they are all removed.  The name
                        may also be a List or Dictionary item.
                        With [!] no error message is given for non-existing
                        variables.
                        One or more items from a List can be removed: 
                                :unlet list[3]    " remove fourth item
                                :unlet list[3:]   " remove fourth item to last
                       One item from a Dictionary can be removed at a time: 
                                :unlet dict['two']
                                :unlet dict.two
                       This is especially useful to clean up used global
                        variables and script-local variables (these are not
                        deleted when the script ends).  Function-local
                        variables are automatically deleted when the function
                        ends.

:unl[et] ${env-name} ...                        :unlet-environment :unlet-$
                        Remove environment variable {env-name}.
                        Can mix {name} and ${env-name} in one :unlet command.
                        No error message is given for a non-existing
                        variable, also without !.
                        If the system does not support deleting an environment
                        variable, it is made empty.

                                                :cons :const E1018
:cons[t] {var-name} = {expr1}
:cons[t] [{name1}, {name2}, ...] = {expr1}
:cons[t] [{name}, ..., ; {lastname}] = {expr1}
:cons[t] {var-name} =<< [trim] {marker}
text...
text...
{marker}
                        Similar to :let, but additionally lock the variable
                        after setting the value.  This is the same as locking
                        the variable with :lockvar just after :let, thus: 
                                :const x = 1
                       is equivalent to: 
                                :let x = 1
                                :lockvar! x
                       NOTE: in Vim9 script :const works differently, see
                        vim9-const
                        This is useful if you want to make sure the variable
                        is not modified.  If the value is a List or Dictionary
                        literal then the items also cannot be changed: 
                                const ll = [1, 2, 3]
                                let ll[1] = 5  " Error!
                       Nested references are not locked: 
                                let lvar = ['a']
                                const lconst = [0, lvar]
                                let lconst[0] = 2  " Error!
                                let lconst[1][0] = 'b'  " OK
                                                       E995
                        :const does not allow to for changing a variable: 
                                :let x = 1
                                :const x = 2  " Error!
                                                       E996
                        Note that environment variables, option values and
                        register values cannot be used here, since they cannot
                        be locked.

:cons[t]
:cons[t] {var-name}
                        If no argument is given or only {var-name} is given,
                        the behavior is the same as :let.

:lockv[ar][!] [depth] {name} ...                        :lockvar :lockv
                        Lock the internal variable {name}.  Locking means that
                        it can no longer be changed (until it is unlocked).
                        A locked variable can be deleted: 
                                :lockvar v
                                :let v = 'asdf'   " fails!
                                :unlet v          " works
                       E741 E940 E1118 E1119 E1120 E1121 E1122
                        If you try to change a locked variable you get an
                        error message: "E741: Value is locked: {name}".
                        If you try to lock or unlock a built-in variable you
                        get an error message: "E940: Cannot lock or unlock
                        variable {name}".

                        [depth] is relevant when locking a List or
                        Dictionary.  It specifies how deep the locking goes:
                                0       Lock the variable {name} but not its
                                        value.
                                1       Lock the List or Dictionary itself,
                                        cannot add or remove items, but can
                                        still change their values.
                                2       Also lock the values, cannot change
                                        the items.  If an item is a List or
                                        Dictionary, cannot add or remove
                                        items, but can still change the
                                        values.
                                3       Like 2 but for the List /
                                        Dictionary in the List /
                                        Dictionary, one level deeper.
                        The default [depth] is 2, thus when {name} is a List
                        or Dictionary the values cannot be changed.

                        Example with [depth] 0: 
                                let mylist = [1, 2, 3]
                                lockvar 0 mylist
                                let mylist[0] = 77      " OK
                                call add(mylist, 4]     " OK
                                let mylist = [7, 8, 9]  " Error!
                                                               E743
                        For unlimited depth use [!] and omit [depth].
                        However, there is a maximum depth of 100 to catch
                        loops.

                        Note that when two variables refer to the same List
                        and you lock one of them, the List will also be
                        locked when used through the other variable.
                        Example: 
                                :let l = [0, 1, 2, 3]
                                :let cl = l
                                :lockvar l
                                :let cl[1] = 99         " won't work!
                       You may want to make a copy of a list to avoid this.
                        See deepcopy().


:unlo[ckvar][!] [depth] {name} ...              :unlockvar :unlo E1246
                        Unlock the internal variable {name}.  Does the
                        opposite of :lockvar.

:if {expr1}                     :if :end :endif :en E171 E579 E580
:en[dif]                Execute the commands until the next matching :else
                        or :endif if {expr1} evaluates to non-zero.
                        Although the short forms work, it is recommended to
                        always use :endif to avoid confusion and to make
                        auto-indenting work properly.

                        From Vim version 4.5 until 5.0, every Ex command in
                        between the :if and :endif is ignored.  These two
                        commands were just to allow for future expansions in a
                        backward compatible way.  Nesting was allowed.  Note
                        that any :else or :elseif was ignored, the else
                        part was not executed either.

                        You can use this to remain compatible with older
                        versions: 
                                :if version >= 500
                                :  version-5-specific-commands
                                :endif
                       The commands still need to be parsed to find the
                        endif.  Sometimes an older Vim has a problem with a
                        new command.  For example, :silent is recognized as
                        a :substitute command.  In that case :execute can
                        avoid problems: 
                                :if version >= 600
                                :  execute "silent 1,$delete"
                                :endif

                        In Vim9 script :endif cannot be shortened, to
                        improve script readability.
                        NOTE: The :append and :insert commands don't work
                        properly in between :if and :endif.

                                                :else :el E581 E583
:el[se]                 Execute the commands until the next matching :else
                        or :endif if they previously were not being
                        executed.
                        In Vim9 script :else cannot be shortened, to
                        improve script readability.

                                        :elseif :elsei E582 E584
:elsei[f] {expr1}       Short for :else :if, with the addition that there
                        is no extra :endif.
                        In Vim9 script :elseif cannot be shortened, to
                        improve script readability.

:wh[ile] {expr1}                        :while :endwhile :wh :endw
                                                E170 E585 E588 E733
:endw[hile]             Repeat the commands between :while and :endwhile,
                        as long as {expr1} evaluates to non-zero.
                        When an error is detected from a command inside the
                        loop, execution continues after the endwhile.
                        Example: 
                                :let lnum = 1
                                :while lnum <= line("$")
                                   :call FixLine(lnum)
                                   :let lnum = lnum + 1
                                :endwhile

                        In Vim9 script :while  and :endwhile cannot be
                        shortened, to improve script readability.
                        NOTE: The :append and :insert commands don't work
                        properly inside a :while and :for loop.

:for {var} in {object}                                  :for E690 E732
:endfo[r]                                               :endfo :endfor
                        Repeat the commands between :for and :endfor for
                        each item in {object}.  {object} can be a List,
                        a Blob or a String. E1177

                        Variable {var} is set to the value of each item.
                        In Vim9 script the loop variable must not have been
                        declared yet, unless when it is a
                        global/window/tab/buffer variable.

                        When an error is detected for a command inside the
                        loop, execution continues after the endfor.
                        Changing {object} inside the loop affects what items
                        are used.  Make a copy if this is unwanted: 
                                :for item in copy(mylist)

                        When {object} is a List and not making a copy, in
                        legacy script Vim stores a reference to the next item
                        in the List before executing the commands with the
                        current item.  Thus the current item can be removed
                        without effect.  Removing any later item means it will
                        not be found.  Thus the following example works (an
                        inefficient way to make a List empty): 
                                for item in mylist
                                   call remove(mylist, 0)
                                endfor
                       Note that reordering the List (e.g., with sort() or
                        reverse()) may have unexpected effects.
                        In Vim9 script the index is used.  If an item before
                        the current one is deleted the next item will be
                        skipped.

                        When {object} is a Blob, Vim always makes a copy to
                        iterate over.  Unlike with List, modifying the
                        Blob does not affect the iteration.

                        In Vim9 script :endfor cannot be shortened, to
                        improve script readability.

:for [{var1}, {var2}, ...] in {listlist}
:endfo[r]                                                       E1140
                        Like :for above, but each item in {listlist} must be
                        a list, of which each item is assigned to {var1},
                        {var2}, etc.  Example: 
                                :for [lnum, col] in [[1, 3], [2, 5], [3, 8]]
                                   :echo getline(lnum)[col]
                                :endfor

                                                :continue :con E586
:con[tinue]             When used inside a :while or :for loop, jumps back
                        to the start of the loop.
                        If it is used after a :try inside the loop but
                        before the matching :finally (if present), the
                        commands following the :finally up to the matching
                        :endtry are executed first.  This process applies to
                        all nested :trys inside the loop.  The outermost
                        :endtry then jumps back to the start of the loop.

                        In Vim9 script :cont is the shortest form, to
                        improve script readability.
                                                :break :brea E587
:brea[k]                When used inside a :while or :for loop, skips to
                        the command after the matching :endwhile or
                        :endfor.
                        If it is used after a :try inside the loop but
                        before the matching :finally (if present), the
                        commands following the :finally up to the matching
                        :endtry are executed first.  This process applies to
                        all nested :trys inside the loop.  The outermost
                        :endtry then jumps to the command after the loop.

                        In Vim9 script :break cannot be shortened, to
                        improve script readability.

:try                                            :try :endt :endtry
                                                E600 E601 E602 E1032
:endt[ry]               Change the error handling for the commands between
                        :try and :endtry including everything being
                        executed across :source commands, function calls,
                        or autocommand invocations.

                        When an error or interrupt is detected and there is
                        a :finally command following, execution continues
                        after the :finally.  Otherwise, or when the
                        :endtry is reached thereafter, the next
                        (dynamically) surrounding :try is checked for
                        a corresponding :finally etc.  Then the script
                        processing is terminated.  Whether a function
                        definition has an "abort" argument does not matter.
                        Example: 
                try | call Unknown() | finally | echomsg "cleanup" | endtry
                echomsg "not reached"

                        Moreover, an error or interrupt (dynamically) inside
                        :try and :endtry is converted to an exception.  It
                        can be caught as if it were thrown by a :throw
                        command (see :catch).  In this case, the script
                        processing is not terminated.

                        The value "Vim:Interrupt" is used for an interrupt
                        exception.  An error in a Vim command is converted
                        to a value of the form "Vim({command}):{errmsg}",
                        other errors are converted to a value of the form
                        "Vim:{errmsg}".  {command} is the full command name,
                        and {errmsg} is the message that is displayed if the
                        error exception is not caught, always beginning with
                        the error number.
                        Examples: 
                try | sleep 100 | catch /^Vim:Interrupt$/ | endtry
                try | edit | catch /^Vim(edit):E\d\+/ | echo "error" | endtry

                        In Vim9 script :endtry cannot be shortened, to
                        improve script readability.

                                        :cat :catch
                                        E603 E604 E605 E654 E1033
:cat[ch] /{pattern}/    The following commands until the next :catch,
                        :finally, or :endtry that belongs to the same
                        :try as the :catch are executed when an exception
                        matching {pattern} is being thrown and has not yet
                        been caught by a previous :catch.  Otherwise, these
                        commands are skipped.
                        When {pattern} is omitted all errors are caught.
                        Examples: 
                :catch /^Vim:Interrupt$/         " catch interrupts (CTRL-C)
                :catch /^Vim\%((\a\+)\)\=:E/     " catch all Vim errors
                :catch /^Vim\%((\a\+)\)\=:/      " catch errors and interrupts
                :catch /^Vim(write):/            " catch all errors in :write
                :catch /^Vim\%((\a\+)\)\=:E123:/ " catch error E123
                :catch /my-exception/            " catch user exception
                :catch /.*/                      " catch everything
                :catch                           " same as /.*/

                        Another character can be used instead of / around the
                        {pattern}, so long as it does not have a special
                        meaning (e.g., '|' or '"') and doesn't occur inside
                        {pattern}. E1067
                        Information about the exception is available in
                        v:exception.  Also see throw-variables.
                        NOTE: It is not reliable to ":catch" the TEXT of
                        an error message because it may vary in different
                        locales.
                        In Vim9 script :catch cannot be shortened, to
                        improve script readability.

                                        :fina :finally E606 E607
:fina[lly]              The following commands until the matching :endtry
                        are executed whenever the part between the matching
                        :try and the :finally is left:  either by falling
                        through to the :finally or by a :continue,
                        :break, :finish, or :return, or by an error or
                        interrupt or exception (see :throw).

                        In Vim9 script :finally cannot be shortened, to
                        improve script readability and avoid confusion with
                        :final.

                                                :th :throw E608 E1129
:th[row] {expr1}        The {expr1} is evaluated and thrown as an exception.
                        If the ":throw" is used after a :try but before the
                        first corresponding :catch, commands are skipped
                        until the first :catch matching {expr1} is reached.
                        If there is no such :catch or if the ":throw" is
                        used after a :catch but before the :finally, the
                        commands following the :finally (if present) up to
                        the matching :endtry are executed.  If the :throw
                        is after the :finally, commands up to the :endtry
                        are skipped.  At the ":endtry", this process applies
                        again for the next dynamically surrounding :try
                        (which may be found in a calling function or sourcing
                        script), until a matching :catch has been found.
                        If the exception is not caught, the command processing
                        is terminated.
                        Example: 
                :try | throw "oops" | catch /^oo/ | echo "caught" | endtry
                       Note that "catch" may need to be on a separate line
                        for when an error causes the parsing to skip the whole
                        line and not see the "|" that separates the commands.

                        In Vim9 script :throw cannot be shortened, to
                        improve script readability.

                                                        :ec :echo
:ec[ho] {expr1} ..      Echoes each {expr1}, with a space in between.  The
                        first {expr1} starts on a new line.
                        Also see :comment.
                        Use "\n" to start a new line.  Use "\r" to move the
                        cursor to the first column.
                        Uses the highlighting set by the :echohl command.
                        Cannot be followed by a comment.
                        Example: 
                :echo "the value of 'shell' is" &shell
                                                       :echo-redraw
                        A later redraw may make the message disappear again.
                        And since Vim mostly postpones redrawing until it's
                        finished with a sequence of commands this happens
                        quite often.  To avoid that a command from before the
                        :echo causes a redraw afterwards (redraws are often
                        postponed until you type something), force a redraw
                        with the :redraw command.  Example: 
                :new | redraw | echo "there is a new window"

                                                        :echon
:echon {expr1} ..       Echoes each {expr1}, without anything added.  Also see
                        :comment.
                        Uses the highlighting set by the :echohl command.
                        Cannot be followed by a comment.
                        Example: 
                                :echon "the value of 'shell' is " &shell

                        Note the difference between using :echo, which is a
                        Vim command, and :!echo, which is an external shell
                        command: 
                :!echo %                --> filename
                       The arguments of ":!" are expanded, see :_%. 
                :!echo "%"              --> filename or "filename"
                       Like the previous example.  Whether you see the double
                        quotes or not depends on your 'shell'. 
                :echo %                 --> nothing
                       The '%' is an illegal character in an expression. 
                :echo "%"               --> %
                       This just echoes the '%' character. 
                :echo expand("%")       --> filename
                       This calls the expand() function to expand the '%'.

                                                        :echoh :echohl
:echoh[l] {name}        Use the highlight group {name} for the following
                        :echo, :echon and :echomsg commands.  Also used
                        for the input() prompt.  Example: 
                :echohl WarningMsg | echo "Don't panic!" | echohl None
                       Don't forget to set the group back to "None",
                        otherwise all following echo's will be highlighted.

                                                        :echom :echomsg
:echom[sg] {expr1} ..   Echo the expression(s) as a true message, saving the
                        message in the message-history.
                        Spaces are placed between the arguments as with the
                        :echo command.  But unprintable characters are
                        displayed, not interpreted.
                        The parsing works slightly different from :echo,
                        more like :execute.  All the expressions are first
                        evaluated and concatenated before echoing anything.
                        If expressions does not evaluate to a Number or
                        String, string() is used to turn it into a string.
                        Uses the highlighting set by the :echohl command.
                        Example: 
                :echomsg "It's a Zizzer Zazzer Zuzz, as you can plainly see."
                       See :echo-redraw to avoid the message disappearing
                        when the screen is redrawn.
                                                        :echoe :echoerr
:echoe[rr] {expr1} ..   Echo the expression(s) as an error message, saving the
                        message in the message-history.  When used in a
                        script or function the line number will be added.
                        Spaces are placed between the arguments as with the
                        :echomsg command.  When used inside a try conditional,
                        the message is raised as an error exception instead
                        (see try-echoerr).
                        Example: 
                :echoerr "This script just failed!"
                       If you just want a highlighted message use :echohl.
                        And to get a beep: 
                :exe "normal \<Esc>"

:echoc[onsole] {expr1} ..                               :echoc :echoconsole
                        Intended for testing: works like :echomsg but when
                        running in the GUI and started from a terminal write
                        the text to stdout.

                                                        :eval
:eval {expr}            Evaluate {expr} and discard the result.  Example: 
                                :eval Getlist()->Filter()->append('$')

                       The expression is supposed to have a side effect,
                        since the resulting value is not used.  In the example
                        the append() call appends the List with text to the
                        buffer.  This is similar to :call but works with any
                        expression.
                        In Vim9 script an expression without an effect will
                        result in error E1207 .  This should help noticing
                        mistakes.

                        The command can be shortened to :ev or :eva, but
                        these are hard to recognize and therefore not to be
                        used.

                        The command cannot be followed by "|" and another
                        command, since "|" is seen as part of the expression.


                                                        :exe :execute
:exe[cute] {expr1} ..   Executes the string that results from the evaluation
                        of {expr1} as an Ex command.
                        Multiple arguments are concatenated, with a space in
                        between.  To avoid the extra space use the ".."
                        operator to concatenate strings into one argument.
                        {expr1} is used as the processed command, command line
                        editing keys are not recognized.
                        Cannot be followed by a comment.
                        Examples: 
                :execute "buffer" nextbuf
                :execute "normal" count .. "w"

                        ":execute" can be used to append a command to commands
                        that don't accept a '|'.  Example: 
                :execute '!ls' | echo "theend"

                       ":execute" is also a nice way to avoid having to type
                        control characters in a Vim script for a ":normal"
                        command: 
                :execute "normal ixxx\<Esc>"
                       This has an <Esc> character, see expr-string.

                        Be careful to correctly escape special characters in
                        file names.  The fnameescape() function can be used
                        for Vim commands, shellescape() for :! commands.
                        Examples: 
                :execute "e " .. fnameescape(filename)
                :execute "!ls " .. shellescape(filename, 1)

                        Note: The executed string may be any command-line, but
                        starting or ending "if", "while" and "for" does not
                        always work, because when commands are skipped the
                        ":execute" is not evaluated and Vim loses track of
                        where blocks start and end.  Also "break" and
                        "continue" should not be inside ":execute".
                        This example does not work, because the ":execute" is
                        not evaluated and Vim does not see the "while", and
                        gives an error for finding an ":endwhile": 
                :if 0
                : execute 'while i > 5'
                :  echo "test"
                : endwhile
                :endif

                        It is allowed to have a "while" or "if" command
                        completely in the executed string: 
                :execute 'while i < 5 | echo i | let i = i + 1 | endwhile'


                                                        :exe-comment
                        ":execute", ":echo" and ":echon" cannot be followed by
                        a comment directly, because they see the '"' as the
                        start of a string.  But, you can use '|' followed by a
                        comment.  Example: 
                :echo "foo" | "this is a comment

==============================================================================
8. Exception handling                                   exception-handling

The Vim script language comprises an exception handling feature.  This section
explains how it can be used in a Vim script.

Exceptions may be raised by Vim on an error or on interrupt, see
catch-errors and catch-interrupt.  You can also explicitly throw an
exception by using the ":throw" command, see throw-catch.


TRY CONDITIONALS                                        try-conditionals

Exceptions can be caught or can cause cleanup code to be executed.  You can
use a try conditional to specify catch clauses (that catch exceptions) and/or
a finally clause (to be executed for cleanup).
   A try conditional begins with a :try command and ends at the matching
:endtry command.  In between, you can use a :catch command to start
a catch clause, or a :finally command to start a finally clause.  There may
be none or multiple catch clauses, but there is at most one finally clause,
which must not be followed by any catch clauses.  The lines before the catch
clauses and the finally clause is called a try block. 

     :try
     :  ...
     :  ...                             TRY BLOCK
     :  ...
     :catch /{pattern}/
     :  ...
     :  ...                             CATCH CLAUSE
     :  ...
     :catch /{pattern}/
     :  ...
     :  ...                             CATCH CLAUSE
     :  ...
     :finally
     :  ...
     :  ...                             FINALLY CLAUSE
     :  ...
     :endtry

The try conditional allows to watch code for exceptions and to take the
appropriate actions.  Exceptions from the try block may be caught.  Exceptions
from the try block and also the catch clauses may cause cleanup actions.
   When no exception is thrown during execution of the try block, the control
is transferred to the finally clause, if present.  After its execution, the
script continues with the line following the ":endtry".
   When an exception occurs during execution of the try block, the remaining
lines in the try block are skipped.  The exception is matched against the
patterns specified as arguments to the ":catch" commands.  The catch clause
after the first matching ":catch" is taken, other catch clauses are not
executed.  The catch clause ends when the next ":catch", ":finally", or
":endtry" command is reached - whatever is first.  Then, the finally clause
(if present) is executed.  When the ":endtry" is reached, the script execution
continues in the following line as usual.
   When an exception that does not match any of the patterns specified by the
":catch" commands is thrown in the try block, the exception is not caught by
that try conditional and none of the catch clauses is executed.  Only the
finally clause, if present, is taken.  The exception pends during execution of
the finally clause.  It is resumed at the ":endtry", so that commands after
the ":endtry" are not executed and the exception might be caught elsewhere,
see try-nesting.
   When during execution of a catch clause another exception is thrown, the
remaining lines in that catch clause are not executed.  The new exception is
not matched against the patterns in any of the ":catch" commands of the same
try conditional and none of its catch clauses is taken.  If there is, however,
a finally clause, it is executed, and the exception pends during its
execution.  The commands following the ":endtry" are not executed.  The new
exception might, however, be caught elsewhere, see try-nesting.
   When during execution of the finally clause (if present) an exception is
thrown, the remaining lines in the finally clause are skipped.  If the finally
clause has been taken because of an exception from the try block or one of the
catch clauses, the original (pending) exception is discarded.  The commands
following the ":endtry" are not executed, and the exception from the finally
clause is propagated and can be caught elsewhere, see try-nesting.

The finally clause is also executed, when a ":break" or ":continue" for
a ":while" loop enclosing the complete try conditional is executed from the
try block or a catch clause.  Or when a ":return" or ":finish" is executed
from the try block or a catch clause of a try conditional in a function or
sourced script, respectively.  The ":break", ":continue", ":return", or
":finish" pends during execution of the finally clause and is resumed when the
":endtry" is reached.  It is, however, discarded when an exception is thrown
from the finally clause.
   When a ":break" or ":continue" for a ":while" loop enclosing the complete
try conditional or when a ":return" or ":finish" is encountered in the finally
clause, the rest of the finally clause is skipped, and the ":break",
":continue", ":return" or ":finish" is executed as usual.  If the finally
clause has been taken because of an exception or an earlier ":break",
":continue", ":return", or ":finish" from the try block or a catch clause,
this pending exception or command is discarded.

For examples see throw-catch and try-finally.


NESTING OF TRY CONDITIONALS                             try-nesting

Try conditionals can be nested arbitrarily.  That is, a complete try
conditional can be put into the try block, a catch clause, or the finally
clause of another try conditional.  If the inner try conditional does not
catch an exception thrown in its try block or throws a new exception from one
of its catch clauses or its finally clause, the outer try conditional is
checked according to the rules above.  If the inner try conditional is in the
try block of the outer try conditional, its catch clauses are checked, but
otherwise only the finally clause is executed.  It does not matter for
nesting, whether the inner try conditional is directly contained in the outer
one, or whether the outer one sources a script or calls a function containing
the inner try conditional.

When none of the active try conditionals catches an exception, just their
finally clauses are executed.  Thereafter, the script processing terminates.
An error message is displayed in case of an uncaught exception explicitly
thrown by a ":throw" command.  For uncaught error and interrupt exceptions
implicitly raised by Vim, the error message(s) or interrupt message are shown
as usual.

For examples see throw-catch.


EXAMINING EXCEPTION HANDLING CODE                       except-examine

Exception handling code can get tricky.  If you are in doubt what happens, set
'verbose' to 13 or use the ":13verbose" command modifier when sourcing your
script file.  Then you see when an exception is thrown, discarded, caught, or
finished.  When using a verbosity level of at least 14, things pending in
a finally clause are also shown.  This information is also given in debug mode
(see debug-scripts).


THROWING AND CATCHING EXCEPTIONS                        throw-catch

You can throw any number or string as an exception.  Use the :throw command
and pass the value to be thrown as argument: 
        :throw 4711
        :throw "string"
                                                       throw-expression
You can also specify an expression argument.  The expression is then evaluated
first, and the result is thrown: 
        :throw 4705 + strlen("string")
        :throw strpart("strings", 0, 6)

An exception might be thrown during evaluation of the argument of the ":throw"
command.  Unless it is caught there, the expression evaluation is abandoned.
The ":throw" command then does not throw a new exception.
   Example: 

        :function! Foo(arg)
        :  try
        :    throw a:arg
        :  catch /foo/
        :  endtry
        :  return 1
        :endfunction
        :
        :function! Bar()
        :  echo "in Bar"
        :  return 4710
        :endfunction
        :
        :throw Foo("arrgh") + Bar()

This throws "arrgh", and "in Bar" is not displayed since Bar() is not
executed. 
        :throw Foo("foo") + Bar()
however displays "in Bar" and throws 4711.

Any other command that takes an expression as argument might also be
abandoned by an (uncaught) exception during the expression evaluation.  The
exception is then propagated to the caller of the command.
   Example: 

        :if Foo("arrgh")
        :  echo "then"
        :else
        :  echo "else"
        :endif

Here neither of "then" or "else" is displayed.

                                                        catch-order
Exceptions can be caught by a try conditional with one or more :catch
commands, see try-conditionals.   The values to be caught by each ":catch"
command can be specified as a pattern argument.  The subsequent catch clause
gets executed when a matching exception is caught.
   Example: 

        :function! Foo(value)
        :  try
        :    throw a:value
        :  catch /^\d\+$/
        :    echo "Number thrown"
        :  catch /.*/
        :    echo "String thrown"
        :  endtry
        :endfunction
        :
        :call Foo(0x1267)
        :call Foo('string')

The first call to Foo() displays "Number thrown", the second "String thrown".
An exception is matched against the ":catch" commands in the order they are
specified.  Only the first match counts.  So you should place the more
specific ":catch" first.  The following order does not make sense: 

        :  catch /.*/
        :    echo "String thrown"
        :  catch /^\d\+$/
        :    echo "Number thrown"

The first ":catch" here matches always, so that the second catch clause is
never taken.

                                                        throw-variables
If you catch an exception by a general pattern, you may access the exact value
in the variable v:exception: 

        :  catch /^\d\+$/
        :    echo "Number thrown.  Value is" v:exception

You may also be interested where an exception was thrown.  This is stored in
v:throwpoint.  Note that "v:exception" and "v:throwpoint" are valid for the
exception most recently caught as long it is not finished.
   Example: 

        :function! Caught()
        :  if v:exception != ""
        :    echo 'Caught "' . v:exception .. '" in ' .. v:throwpoint
        :  else
        :    echo 'Nothing caught'
        :  endif
        :endfunction
        :
        :function! Foo()
        :  try
        :    try
        :      try
        :        throw 4711
        :      finally
        :        call Caught()
        :      endtry
        :    catch /.*/
        :      call Caught()
        :      throw "oops"
        :    endtry
        :  catch /.*/
        :    call Caught()
        :  finally
        :    call Caught()
        :  endtry
        :endfunction
        :
        :call Foo()

This displays 

        Nothing caught
        Caught "4711" in function Foo, line 4
        Caught "oops" in function Foo, line 10
        Nothing caught

A practical example:  The following command ":LineNumber" displays the line
number in the script or function where it has been used: 

        :function! LineNumber()
        :    return substitute(v:throwpoint, '.*\D\(\d\+\).*', '\1', "")
        :endfunction
        :command! LineNumber try | throw "" | catch | echo LineNumber() | endtry

                                                        try-nested
An exception that is not caught by a try conditional can be caught by
a surrounding try conditional: 

        :try
        :  try
        :    throw "foo"
        :  catch /foobar/
        :    echo "foobar"
        :  finally
        :    echo "inner finally"
        :  endtry
        :catch /foo/
        :  echo "foo"
        :endtry

The inner try conditional does not catch the exception, just its finally
clause is executed.  The exception is then caught by the outer try
conditional.  The example displays "inner finally" and then "foo".

                                                        throw-from-catch
You can catch an exception and throw a new one to be caught elsewhere from the
catch clause: 

        :function! Foo()
        :  throw "foo"
        :endfunction
        :
        :function! Bar()
        :  try
        :    call Foo()
        :  catch /foo/
        :    echo "Caught foo, throw bar"
        :    throw "bar"
        :  endtry
        :endfunction
        :
        :try
        :  call Bar()
        :catch /.*/
        :  echo "Caught" v:exception
        :endtry

This displays "Caught foo, throw bar" and then "Caught bar".

                                                        rethrow
There is no real rethrow in the Vim script language, but you may throw
"v:exception" instead: 

        :function! Bar()
        :  try
        :    call Foo()
        :  catch /.*/
        :    echo "Rethrow" v:exception
        :    throw v:exception
        :  endtry
        :endfunction
                                                       try-echoerr
Note that this method cannot be used to "rethrow" Vim error or interrupt
exceptions, because it is not possible to fake Vim internal exceptions.
Trying so causes an error exception.  You should throw your own exception
denoting the situation.  If you want to cause a Vim error exception containing
the original error exception value, you can use the :echoerr command: 

        :try
        :  try
        :    asdf
        :  catch /.*/
        :    echoerr v:exception
        :  endtry
        :catch /.*/
        :  echo v:exception
        :endtry

This code displays

        Vim(echoerr):Vim:E492: Not an editor command:   asdf 


CLEANUP CODE                                            try-finally

Scripts often change global settings and restore them at their end.  If the
user however interrupts the script by pressing CTRL-C, the settings remain in
an inconsistent state.  The same may happen to you in the development phase of
a script when an error occurs or you explicitly throw an exception without
catching it.  You can solve these problems by using a try conditional with
a finally clause for restoring the settings.  Its execution is guaranteed on
normal control flow, on error, on an explicit ":throw", and on interrupt.
(Note that errors and interrupts from inside the try conditional are converted
to exceptions.  When not caught, they terminate the script after the finally
clause has been executed.)
Example: 

        :try
        :  let s:saved_ts = &ts
        :  set ts=17
        :
        :  " Do the hard work here.
        :
        :finally
        :  let &ts = s:saved_ts
        :  unlet s:saved_ts
        :endtry

This method should be used locally whenever a function or part of a script
changes global settings which need to be restored on failure or normal exit of
that function or script part.

                                                        break-finally
Cleanup code works also when the try block or a catch clause is left by
a ":continue", ":break", ":return", or ":finish".
   Example: 

        :let first = 1
        :while 1
        :  try
        :    if first
        :      echo "first"
        :      let first = 0
        :      continue
        :    else
        :      throw "second"
        :    endif
        :  catch /.*/
        :    echo v:exception
        :    break
        :  finally
        :    echo "cleanup"
        :  endtry
        :  echo "still in while"
        :endwhile
        :echo "end"

This displays "first", "cleanup", "second", "cleanup", and "end". 

        :function! Foo()
        :  try
        :    return 4711
        :  finally
        :    echo "cleanup\n"
        :  endtry
        :  echo "Foo still active"
        :endfunction
        :
        :echo Foo() "returned by Foo"

This displays "cleanup" and "4711 returned by Foo".  You don't need to add an
extra ":return" in the finally clause.  (Above all, this would override the
return value.)

                                                        except-from-finally
Using either of ":continue", ":break", ":return", ":finish", or ":throw" in
a finally clause is possible, but not recommended since it abandons the
cleanup actions for the try conditional.  But, of course, interrupt and error
exceptions might get raised from a finally clause.
   Example where an error in the finally clause stops an interrupt from
working correctly: 

        :try
        :  try
        :    echo "Press CTRL-C for interrupt"
        :    while 1
        :    endwhile
        :  finally
        :    unlet novar
        :  endtry
        :catch /novar/
        :endtry
        :echo "Script still running"
        :sleep 1

If you need to put commands that could fail into a finally clause, you should
think about catching or ignoring the errors in these commands, see
catch-errors and ignore-errors.


CATCHING ERRORS                                         catch-errors

If you want to catch specific errors, you just have to put the code to be
watched in a try block and add a catch clause for the error message.  The
presence of the try conditional causes all errors to be converted to an
exception.  No message is displayed and v:errmsg is not set then.  To find
the right pattern for the ":catch" command, you have to know how the format of
the error exception is.
   Error exceptions have the following format: 

        Vim({cmdname}):{errmsg}
or 
        Vim:{errmsg}

{cmdname} is the name of the command that failed; the second form is used when
the command name is not known.  {errmsg} is the error message usually produced
when the error occurs outside try conditionals.  It always begins with
a capital "E", followed by a two or three-digit error number, a colon, and
a space.

Examples:

The command 
        :unlet novar
normally produces the error message 
        E108: No such variable: "novar"
which is converted inside try conditionals to an exception 
        Vim(unlet):E108: No such variable: "novar"

The command 
        :dwim
normally produces the error message 
        E492: Not an editor command: dwim
which is converted inside try conditionals to an exception 
        Vim:E492: Not an editor command: dwim

You can catch all ":unlet" errors by a 
        :catch /^Vim(unlet):/
or all errors for misspelled command names by a 
        :catch /^Vim:E492:/

Some error messages may be produced by different commands: 
        :function nofunc
and 
        :delfunction nofunc
both produce the error message 
        E128: Function name must start with a capital: nofunc
which is converted inside try conditionals to an exception 
        Vim(function):E128: Function name must start with a capital: nofunc
or 
        Vim(delfunction):E128: Function name must start with a capital: nofunc
respectively.  You can catch the error by its number independently on the
command that caused it if you use the following pattern: 
        :catch /^Vim(\a\+):E128:/

Some commands like 
        :let x = novar
produce multiple error messages, here: 
        E121: Undefined variable: novar
        E15: Invalid expression:  novar
Only the first is used for the exception value, since it is the most specific
one (see except-several-errors).  So you can catch it by 
        :catch /^Vim(\a\+):E121:/

You can catch all errors related to the name "nofunc" by 
        :catch /\<nofunc\>/

You can catch all Vim errors in the ":write" and ":read" commands by 
        :catch /^Vim(\(write\|read\)):E\d\+:/

You can catch all Vim errors by the pattern 
        :catch /^Vim\((\a\+)\)\=:E\d\+:/

                                                        catch-text
NOTE: You should never catch the error message text itself: 
        :catch /No such variable/
only works in the English locale, but not when the user has selected
a different language by the :language command.  It is however helpful to
cite the message text in a comment: 
        :catch /^Vim(\a\+):E108:/   " No such variable


IGNORING ERRORS                                         ignore-errors

You can ignore errors in a specific Vim command by catching them locally: 

        :try
        :  write
        :catch
        :endtry

But you are strongly recommended NOT to use this simple form, since it could
catch more than you want.  With the ":write" command, some autocommands could
be executed and cause errors not related to writing, for instance: 

        :au BufWritePre * unlet novar

There could even be such errors you are not responsible for as a script
writer: a user of your script might have defined such autocommands.  You would
then hide the error from the user.
   It is much better to use 

        :try
        :  write
        :catch /^Vim(write):/
        :endtry

which only catches real write errors.  So catch only what you'd like to ignore
intentionally.

For a single command that does not cause execution of autocommands, you could
even suppress the conversion of errors to exceptions by the ":silent!"
command: 
        :silent! nunmap k
This works also when a try conditional is active.


CATCHING INTERRUPTS                                     catch-interrupt

When there are active try conditionals, an interrupt (CTRL-C) is converted to
the exception "Vim:Interrupt".  You can catch it like every exception.  The
script is not terminated, then.
   Example: 

        :function! TASK1()
        :  sleep 10
        :endfunction

        :function! TASK2()
        :  sleep 20
        :endfunction

        :while 1
        :  let command = input("Type a command: ")
        :  try
        :    if command == ""
        :      continue
        :    elseif command == "END"
        :      break
        :    elseif command == "TASK1"
        :      call TASK1()
        :    elseif command == "TASK2"
        :      call TASK2()
        :    else
        :      echo "\nIllegal command:" command
        :      continue
        :    endif
        :  catch /^Vim:Interrupt$/
        :    echo "\nCommand interrupted"
        :    " Caught the interrupt.  Continue with next prompt.
        :  endtry
        :endwhile

You can interrupt a task here by pressing CTRL-C; the script then asks for
a new command.  If you press CTRL-C at the prompt, the script is terminated.

For testing what happens when CTRL-C would be pressed on a specific line in
your script, use the debug mode and execute the >quit or >interrupt
command on that line.  See debug-scripts.


CATCHING ALL                                            catch-all

The commands 

        :catch /.*/
        :catch //
        :catch

catch everything, error exceptions, interrupt exceptions and exceptions
explicitly thrown by the :throw command.  This is useful at the top level of
a script in order to catch unexpected things.
   Example: 

        :try
        :
        :  " do the hard work here
        :
        :catch /MyException/
        :
        :  " handle known problem
        :
        :catch /^Vim:Interrupt$/
        :    echo "Script interrupted"
        :catch /.*/
        :  echo "Internal error (" .. v:exception .. ")"
        :  echo " - occurred at " .. v:throwpoint
        :endtry
        :" end of script

Note: Catching all might catch more things than you want.  Thus, you are
strongly encouraged to catch only for problems that you can really handle by
specifying a pattern argument to the ":catch".
   Example: Catching all could make it nearly impossible to interrupt a script
by pressing CTRL-C: 

        :while 1
        :  try
        :    sleep 1
        :  catch
        :  endtry
        :endwhile


EXCEPTIONS AND AUTOCOMMANDS                             except-autocmd

Exceptions may be used during execution of autocommands.  Example: 

        :autocmd User x try
        :autocmd User x   throw "Oops!"
        :autocmd User x catch
        :autocmd User x   echo v:exception
        :autocmd User x endtry
        :autocmd User x throw "Arrgh!"
        :autocmd User x echo "Should not be displayed"
        :
        :try
        :  doautocmd User x
        :catch
        :  echo v:exception
        :endtry

This displays "Oops!" and "Arrgh!".

                                                        except-autocmd-Pre
For some commands, autocommands get executed before the main action of the
command takes place.  If an exception is thrown and not caught in the sequence
of autocommands, the sequence and the command that caused its execution are
abandoned and the exception is propagated to the caller of the command.
   Example: 

        :autocmd BufWritePre * throw "FAIL"
        :autocmd BufWritePre * echo "Should not be displayed"
        :
        :try
        :  write
        :catch
        :  echo "Caught:" v:exception "from" v:throwpoint
        :endtry

Here, the ":write" command does not write the file currently being edited (as
you can see by checking 'modified'), since the exception from the BufWritePre
autocommand abandons the ":write".  The exception is then caught and the
script displays: 

        Caught: FAIL from BufWrite Auto commands for "*"

                                                        except-autocmd-Post
For some commands, autocommands get executed after the main action of the
command has taken place.  If this main action fails and the command is inside
an active try conditional, the autocommands are skipped and an error exception
is thrown that can be caught by the caller of the command.
   Example: 

        :autocmd BufWritePost * echo "File successfully written!"
        :
        :try
        :  write /i/m/p/o/s/s/i/b/l/e
        :catch
        :  echo v:exception
        :endtry

This just displays: 

        Vim(write):E212: Can't open file for writing (/i/m/p/o/s/s/i/b/l/e)

If you really need to execute the autocommands even when the main action
fails, trigger the event from the catch clause.
   Example: 

        :autocmd BufWritePre  * set noreadonly
        :autocmd BufWritePost * set readonly
        :
        :try
        :  write /i/m/p/o/s/s/i/b/l/e
        :catch
        :  doautocmd BufWritePost /i/m/p/o/s/s/i/b/l/e
        :endtry

You can also use ":silent!": 

        :let x = "ok"
        :let v:errmsg = ""
        :autocmd BufWritePost * if v:errmsg != ""
        :autocmd BufWritePost *   let x = "after fail"
        :autocmd BufWritePost * endif
        :try
        :  silent! write /i/m/p/o/s/s/i/b/l/e
        :catch
        :endtry
        :echo x

This displays "after fail".

If the main action of the command does not fail, exceptions from the
autocommands will be catchable by the caller of the command:  

        :autocmd BufWritePost * throw ":-("
        :autocmd BufWritePost * echo "Should not be displayed"
        :
        :try
        :  write
        :catch
        :  echo v:exception
        :endtry

                                                        except-autocmd-Cmd
For some commands, the normal action can be replaced by a sequence of
autocommands.  Exceptions from that sequence will be catchable by the caller
of the command.
   Example:  For the ":write" command, the caller cannot know whether the file
had actually been written when the exception occurred.  You need to tell it in
some way. 

        :if !exists("cnt")
        :  let cnt = 0
        :
        :  autocmd BufWriteCmd * if &modified
        :  autocmd BufWriteCmd *   let cnt = cnt + 1
        :  autocmd BufWriteCmd *   if cnt % 3 == 2
        :  autocmd BufWriteCmd *     throw "BufWriteCmdError"
        :  autocmd BufWriteCmd *   endif
        :  autocmd BufWriteCmd *   write | set nomodified
        :  autocmd BufWriteCmd *   if cnt % 3 == 0
        :  autocmd BufWriteCmd *     throw "BufWriteCmdError"
        :  autocmd BufWriteCmd *   endif
        :  autocmd BufWriteCmd *   echo "File successfully written!"
        :  autocmd BufWriteCmd * endif
        :endif
        :
        :try
        :       write
        :catch /^BufWriteCmdError$/
        :  if &modified
        :    echo "Error on writing (file contents not changed)"
        :  else
        :    echo "Error after writing"
        :  endif
        :catch /^Vim(write):/
        :    echo "Error on writing"
        :endtry

When this script is sourced several times after making changes, it displays
first 
        File successfully written!
then 
        Error on writing (file contents not changed)
then 
        Error after writing
etc.

                                                        except-autocmd-ill
You cannot spread a try conditional over autocommands for different events.
The following code is ill-formed: 

        :autocmd BufWritePre  * try
        :
        :autocmd BufWritePost * catch
        :autocmd BufWritePost *   echo v:exception
        :autocmd BufWritePost * endtry
        :
        :write


EXCEPTION HIERARCHIES AND PARAMETERIZED EXCEPTIONS      except-hier-param

Some programming languages allow to use hierarchies of exception classes or to
pass additional information with the object of an exception class.  You can do
similar things in Vim.
   In order to throw an exception from a hierarchy, just throw the complete
class name with the components separated by a colon, for instance throw the
string "EXCEPT:MATHERR:OVERFLOW" for an overflow in a mathematical library.
   When you want to pass additional information with your exception class, add
it in parentheses, for instance throw the string "EXCEPT:IO:WRITEERR(myfile)"
for an error when writing "myfile".
   With the appropriate patterns in the ":catch" command, you can catch for
base classes or derived classes of your hierarchy.  Additional information in
parentheses can be cut out from v:exception with the ":substitute" command.
   Example: 

        :function! CheckRange(a, func)
        :  if a:a < 0
        :    throw "EXCEPT:MATHERR:RANGE(" .. a:func .. ")"
        :  endif
        :endfunction
        :
        :function! Add(a, b)
        :  call CheckRange(a:a, "Add")
        :  call CheckRange(a:b, "Add")
        :  let c = a:a + a:b
        :  if c < 0
        :    throw "EXCEPT:MATHERR:OVERFLOW"
        :  endif
        :  return c
        :endfunction
        :
        :function! Div(a, b)
        :  call CheckRange(a:a, "Div")
        :  call CheckRange(a:b, "Div")
        :  if (a:b == 0)
        :    throw "EXCEPT:MATHERR:ZERODIV"
        :  endif
        :  return a:a / a:b
        :endfunction
        :
        :function! Write(file)
        :  try
        :    execute "write" fnameescape(a:file)
        :  catch /^Vim(write):/
        :    throw "EXCEPT:IO(" .. getcwd() .. ", " .. a:file .. "):WRITEERR"
        :  endtry
        :endfunction
        :
        :try
        :
        :  " something with arithmetic and I/O
        :
        :catch /^EXCEPT:MATHERR:RANGE/
        :  let function = substitute(v:exception, '.*(\(\a\+\)).*', '\1', "")
        :  echo "Range error in" function
        :
        :catch /^EXCEPT:MATHERR/        " catches OVERFLOW and ZERODIV
        :  echo "Math error"
        :
        :catch /^EXCEPT:IO/
        :  let dir = substitute(v:exception, '.*(\(.\+\),\s*.\+).*', '\1', "")
        :  let file = substitute(v:exception, '.*(.\+,\s*\(.\+\)).*', '\1', "")
        :  if file !~ '^/'
        :    let file = dir .. "/" .. file
        :  endif
        :  echo 'I/O error for "' .. file .. '"'
        :
        :catch /^EXCEPT/
        :  echo "Unspecified error"
        :
        :endtry

The exceptions raised by Vim itself (on error or when pressing CTRL-C) use
a flat hierarchy:  they are all in the "Vim" class.  You cannot throw yourself
exceptions with the "Vim" prefix; they are reserved for Vim.
   Vim error exceptions are parameterized with the name of the command that
failed, if known.  See catch-errors.


PECULIARITIES
                                                        except-compat
The exception handling concept requires that the command sequence causing the
exception is aborted immediately and control is transferred to finally clauses
and/or a catch clause.

In the Vim script language there are cases where scripts and functions
continue after an error: in functions without the "abort" flag or in a command
after ":silent!", control flow goes to the following line, and outside
functions, control flow goes to the line following the outermost ":endwhile"
or ":endif".  On the other hand, errors should be catchable as exceptions
(thus, requiring the immediate abortion).

This problem has been solved by converting errors to exceptions and using
immediate abortion (if not suppressed by ":silent!") only when a try
conditional is active.  This is no restriction since an (error) exception can
be caught only from an active try conditional.  If you want an immediate
termination without catching the error, just use a try conditional without
catch clause.  (You can cause cleanup code being executed before termination
by specifying a finally clause.)

When no try conditional is active, the usual abortion and continuation
behavior is used instead of immediate abortion.  This ensures compatibility of
scripts written for Vim 6.1 and earlier.

However, when sourcing an existing script that does not use exception handling
commands (or when calling one of its functions) from inside an active try
conditional of a new script, you might change the control flow of the existing
script on error.  You get the immediate abortion on error and can catch the
error in the new script.  If however the sourced script suppresses error
messages by using the ":silent!" command (checking for errors by testing
v:errmsg if appropriate), its execution path is not changed.  The error is
not converted to an exception.  (See :silent.)  So the only remaining cause
where this happens is for scripts that don't care about errors and produce
error messages.  You probably won't want to use such code from your new
scripts.

                                                        except-syntax-err
Syntax errors in the exception handling commands are never caught by any of
the ":catch" commands of the try conditional they belong to.  Its finally
clauses, however, is executed.
   Example: 

        :try
        :  try
        :    throw 4711
        :  catch /\(/
        :    echo "in catch with syntax error"
        :  catch
        :    echo "inner catch-all"
        :  finally
        :    echo "inner finally"
        :  endtry
        :catch
        :  echo 'outer catch-all caught "' .. v:exception .. '"'
        :  finally
        :    echo "outer finally"
        :endtry

This displays: 
    inner finally
    outer catch-all caught "Vim(catch):E54: Unmatched \("
    outer finally
The original exception is discarded and an error exception is raised, instead.

                                                        except-single-line
The ":try", ":catch", ":finally", and ":endtry" commands can be put on
a single line, but then syntax errors may make it difficult to recognize the
"catch" line, thus you better avoid this.
   Example: 
        :try | unlet! foo # | catch | endtry
raises an error exception for the trailing characters after the ":unlet!"
argument, but does not see the ":catch" and ":endtry" commands, so that the
error exception is discarded and the "E488: Trailing characters" message gets
displayed.

                                                        except-several-errors
When several errors appear in a single command, the first error message is
usually the most specific one and therefore converted to the error exception.
   Example: 
        echo novar
causes 
        E121: Undefined variable: novar
        E15: Invalid expression: novar
The value of the error exception inside try conditionals is: 
        Vim(echo):E121: Undefined variable: novar
                                                       except-syntax-error
But when a syntax error is detected after a normal error in the same command,
the syntax error is used for the exception being thrown.
   Example: 
        unlet novar #
causes 
        E108: No such variable: "novar"
        E488: Trailing characters
The value of the error exception inside try conditionals is: 
        Vim(unlet):E488: Trailing characters
This is done because the syntax error might change the execution path in a way
not intended by the user.  Example: 
        try
            try | unlet novar # | catch | echo v:exception | endtry
        catch /.*/
            echo "outer catch:" v:exception
        endtry
This displays "outer catch: Vim(unlet):E488: Trailing characters", and then
a "E600: Missing :endtry" error message is given, see except-single-line.

==============================================================================
9. Examples                                             eval-examples

Printing in Binary 

  :" The function Nr2Bin() returns the binary string representation of a number.
  :func Nr2Bin(nr)
  :  let n = a:nr
  :  let r = ""
  :  while n
  :    let r = '01'[n % 2] .. r
  :    let n = n / 2
  :  endwhile
  :  return r
  :endfunc

  :" The function String2Bin() converts each character in a string to a
  :" binary string, separated with dashes.
  :func String2Bin(str)
  :  let out = ''
  :  for ix in range(strlen(a:str))
  :    let out = out .. '-' .. Nr2Bin(char2nr(a:str[ix]))
  :  endfor
  :  return out[1:]
  :endfunc

Example of its use: 
  :echo Nr2Bin(32)
result: "100000" 
  :echo String2Bin("32")
result: "110011-110010"


Sorting lines 

This example sorts lines with a specific compare function. 

  :func SortBuffer()
  :  let lines = getline(1, '$')
  :  call sort(lines, function("Strcmp"))
  :  call setline(1, lines)
  :endfunction

As a one-liner: 
  :call setline(1, sort(getline(1, '$'), function("Strcmp")))


scanf() replacement 
                                                        sscanf
There is no sscanf() function in Vim.  If you need to extract parts from a
line, you can use matchstr() and substitute() to do it.  This example shows
how to get the file name, line number and column number out of a line like
"foobar.txt, 123, 45". 
   :" Set up the match bit
   :let mx='\(\f\+\),\s*\(\d\+\),\s*\(\d\+\)'
   :"get the part matching the whole expression
   :let l = matchstr(line, mx)
   :"get each item out of the match
   :let file = substitute(l, mx, '\1', '')
   :let lnum = substitute(l, mx, '\2', '')
   :let col = substitute(l, mx, '\3', '')

The input is in the variable "line", the results in the variables "file",
"lnum" and "col". (idea from Michael Geddes)


getting the scriptnames in a Dictionary 
                                                scriptnames-dictionary
The :scriptnames command can be used to get a list of all script files that
have been sourced.  There is no equivalent function or variable for this
(because it's rarely needed).  In case you need to manipulate the list this
code can be used: 
    " Get the output of ":scriptnames" in the scriptnames_output variable.
    let scriptnames_output = ''
    redir => scriptnames_output
    silent scriptnames
    redir END

    " Split the output into lines and parse each line.  Add an entry to the
    " "scripts" dictionary.
    let scripts = {}
    for line in split(scriptnames_output, "\n")
      " Only do non-blank lines.
      if line =~ '\S'
        " Get the first number in the line.
        let nr = matchstr(line, '\d\+')
        " Get the file name, remove the script number " 123: ".
        let name = substitute(line, '.\+:\s*', '', '')
        " Add an item to the Dictionary
        let scripts[nr] = name
      endif
    endfor
    unlet scriptnames_output

==============================================================================
10. Vim script versions         vimscript-version vimscript-versions
                                                        scriptversion
Over time many features have been added to Vim script.  This includes Ex
commands, functions, variable types, etc.  Each individual feature can be
checked with the has() and exists() functions.

Sometimes old syntax of functionality gets in the way of making Vim better.
When support is taken away this will break older Vim scripts.  To make this
explicit the :scriptversion command can be used.  When a Vim script is not
compatible with older versions of Vim this will give an explicit error,
instead of failing in mysterious ways.

When using a legacy function, defined with :function, in Vim9 script then
scriptversion 4 is used.

                                                        scriptversion-1  
 :scriptversion 1
       This is the original Vim script, same as not using a :scriptversion
        command.  Can be used to go back to old syntax for a range of lines.
        Test for support with: 
                has('vimscript-1')

                                                       scriptversion-2  
 :scriptversion 2
       String concatenation with "." is not supported, use ".." instead.
        This avoids the ambiguity using "." for Dict member access and
        floating point numbers.  Now ".5" means the number 0.5.

                                                        scriptversion-3  
 :scriptversion 3
       All vim-variables must be prefixed by "v:".  E.g. "version" doesn't
        work as v:version anymore, it can be used as a normal variable.
        Same for some obvious names as "count" and others.

        Test for support with: 
                has('vimscript-3')

                                                        scriptversion-4  
 :scriptversion 4
       Numbers with a leading zero are not recognized as octal.  "0o" or "0O"
        is still recognized as octal.  With the
        previous version you get: 
                echo 017   " displays 15 (octal)
                echo 0o17  " displays 15 (octal)
                echo 018   " displays 18 (decimal)
       with script version 4: 
                echo 017   " displays 17 (decimal)
                echo 0o17  " displays 15 (octal)
                echo 018   " displays 18 (decimal)
       Also, it is possible to use single quotes inside numbers to make them
        easier to read: 
                echo 1'000'000
       The quotes must be surrounded by digits.

        Test for support with: 
                has('vimscript-4')

==============================================================================
11. No +eval feature                            no-eval-feature

When the +eval feature was disabled at compile time, none of the expression
evaluation commands are available.  To prevent this from causing Vim scripts
to generate all kinds of errors, the ":if" and ":endif" commands are still
recognized, though the argument of the ":if" and everything between the ":if"
and the matching ":endif" is ignored.  Nesting of ":if" blocks is allowed, but
only if the commands are at the start of the line.  The ":else" command is not
recognized.

Example of how to avoid executing commands when the +eval feature is
missing: 

        :if 1
        :  echo "Expression evaluation is compiled in"
        :else
        :  echo "You will _never_ see this message"
        :endif

To execute a command only when the +eval feature is disabled can be done in
two ways.  The simplest is to exit the script (or Vim) prematurely: 
        if 1
           echo "commands executed with +eval"
           finish
        endif
        args  " command executed without +eval

If you do not want to abort loading the script you can use a trick, as this
example shows: 

        silent! while 0
          set history=111
        silent! endwhile

When the +eval feature is available the command is skipped because of the
"while 0".  Without the +eval feature the "while 0" is an error, which is
silently ignored, and the command is executed.

==============================================================================
12. The sandbox                                 eval-sandbox sandbox

The 'foldexpr', 'formatexpr', 'includeexpr', 'indentexpr', 'statusline' and
'foldtext' options may be evaluated in a sandbox.  This means that you are
protected from these expressions having nasty side effects.  This gives some
safety for when these options are set from a modeline.  It is also used when
the command from a tags file is executed and for CTRL-R = in the command line.
The sandbox is also used for the :sandbox command.
                                                                E48
These items are not allowed in the sandbox:
        - changing the buffer text
        - defining or changing mapping, autocommands, user commands
        - setting certain options (see option-summary)
        - setting certain v: variables (see v:var)  E794
        - executing a shell command
        - reading or writing a file
        - jumping to another buffer or editing a file
        - executing Python, Perl, etc. commands
This is not guaranteed 100% secure, but it should block most attacks.

                                                        :san :sandbox
:san[dbox] {cmd}        Execute {cmd} in the sandbox.  Useful to evaluate an
                        option that may have been set from a modeline, e.g.
                        'foldexpr'.

                                                        sandbox-option
A few options contain an expression.  When this expression is evaluated it may
have to be done in the sandbox to avoid a security risk.  But the sandbox is
restrictive, thus this only happens when the option was set from an insecure
location.  Insecure in this context are:
- sourcing a .vimrc or .exrc in the current directory
- while executing in the sandbox
- value coming from a modeline
- executing a function that was defined in the sandbox

Note that when in the sandbox and saving an option value and restoring it, the
option will still be marked as it was set in the sandbox.

==============================================================================
13. Textlock                                                    textlock

In a few situations it is not allowed to change the text in the buffer, jump
to another window and some other things that might confuse or break what Vim
is currently doing.  This mostly applies to things that happen when Vim is
actually doing something else.  For example, evaluating the 'balloonexpr' may
happen any moment the mouse cursor is resting at some position.

This is not allowed when the textlock is active:
        - changing the buffer text
        - jumping to another buffer or window
        - editing another file
        - closing a window or quitting Vim
        - etc.


 vim:tw=78:ts=8:noet:ft=help:norl:

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