*usr_41.txt*    For Vim version 9.0.  Last change: 2022 Dec 20

                     VIM USER MANUAL - by Bram Moolenaar

                              Write a Vim script


The Vim script language is used for the startup vimrc file, syntax files, and
many other things.  This chapter explains the items that can be used in a Vim
script.  There are a lot of them, therefore this is a long chapter.

|41.1|  Introduction
|41.2|  Variables
|41.3|  Expressions
|41.4|  Conditionals
|41.5|  Executing an expression
|41.6|  Using functions
|41.7|  Defining a function
|41.8|  Lists and Dictionaries
|41.9|  White space
|41.10| Line continuation
|41.11| Comments
|41.12| Fileformat

     Next chapter: |usr_42.txt|  Add new menus
 Previous chapter: |usr_40.txt|  Make new commands
Table of contents: |usr_toc.txt|

==============================================================================
*41.1*  Introduction                            *vim-script-intro* *script*

Your first experience with Vim scripts is the vimrc file.  Vim reads it when
it starts up and executes the commands.  You can set options to the values you
prefer, define mappings, select plugins and much more.   You can use any colon
command in it (commands that start with a ":"; these are sometimes referred to
as Ex commands or command-line commands).

Syntax files are also Vim scripts.  As are files that set options for a
specific file type.  A complicated macro can be defined by a separate Vim
script file.  You can think of other uses yourself.

Vim script comes in two flavors: legacy and |Vim9|.  Since this help file is
for new users, we'll teach you the newer and more convenient |Vim9| syntax.
While legacy script is particularly for Vim, |Vim9| script looks more like
other languages, such as JavaScript and TypeScript.

To try out Vim script the best way is to edit a script file and source it.
Basically: >
        :edit test.vim
        [insert the script lines you want]
        :w
        :source %

Let's start with a simple example: >

        vim9script
        var i = 1
        while i < 5
          echo "count is" i
          i += 1
        endwhile
<
The output of the example code is:

        count is 1 ~
        count is 2 ~
        count is 3 ~
        count is 4 ~

In the first line the `vim9script` command makes clear this is a new, |Vim9|
script file.  That matters for how the rest of the file is used.  It is
recommended to put it in the very fist line, before any comments.
                                                        *vim9-declarations*
The `var i = 1` command declares the "i" variable and initializes it.  The
generic form is: >

        var {name} = {expression}

In this case the variable name is "i" and the expression is a simple value,
the number one.

The `while` command starts a loop.  The generic form is: >

        while {condition}
          {statements}
        endwhile

The statements until the matching `endwhile` are executed for as long as the
condition is true.  The condition used here is the expression "i < 5".  This
is true when the variable i is smaller than five.
        Note:
        If you happen to write a while loop that keeps on running, you can
        interrupt it by pressing CTRL-C (CTRL-Break on MS-Windows).

The `echo` command prints its arguments.  In this case the string "count is"
and the value of the variable i.  Since i is one, this will print:

        count is 1 ~

Then there is the `i += 1` command.  This does the same thing as "i = i + 1",
it adds one to the variable i and assigns the new value to the same variable.

The example was given to explain the commands, but would you really want to
make such a loop, it can be written much more compact: >

        for i in range(1, 4)
          echo $"count is {i}"
        endfor

We won't explain how `for`, `range()`and `$"string"` work until later.  Follow
the links if you are impatient.


TRYING OUT EXAMPLES

You can easily try out most examples in these help files without saving the
commands to a file.  For example, to try out the "for" loop above do this:
1. position the cursor on the "for"
2. start Visual mode with "v"
3. move down to the "endfor"
4. press colon, then "so" and Enter

After pressing colon you will see ":'<,'>", which is the range of the Visually
selected text.

For some commands it matters they are executed as in |Vim9| script.  But typed
commands normally use legacy script syntax, such as the example below that
causes the E1004 error.  For that use this fourth step:
4. press colon, then "vim9 so" and Enter

"vim9" is short for `vim9cmd`, which is a command modifier to execute the
following command in |Vim9| syntax.

Note that this won't work for examples that require a script context.


FOUR KINDS OF NUMBERS

Numbers can be decimal, hexadecimal, octal and binary.

A hexadecimal number starts with "0x" or "0X".  For example "0x1f" is decimal
31 and "0x1234" is decimal 4660.

An octal number starts with "0o", "0O".  "0o17" is decimal 15.

A binary number starts with "0b" or "0B".  For example "0b101" is decimal 5.

A decimal number is just digits.  Careful: In legacy script don't put a zero
before a decimal number, it will be interpreted as an octal number!  That's
one reason to use |Vim9| script.

The `echo` command evaluates its argument and when it is a number always
prints the decimal form.  Example: >

        echo 0x7f 0o36
<       127 30 ~

A number is made negative with a minus sign.  This also works for hexadecimal,
octal and binary numbers: >

        echo -0x7f
<       -127 ~

A minus sign is also used for subtraction.  This can sometimes lead to
confusion.  If we put a minus sign before both numbers we get an error: >

        echo -0x7f -0o36
<       E1004: White space required before and after '-' at "-0o36" ~

Note: if you are not using a |Vim9| script to try out these commands but type
them directly, they will be executed as legacy script.  Then the echo command
sees the second minus sign as subtraction.  To get the error, prefix the
command with `vim9cmd`: >

        vim9cmd echo -0x7f -0o36
<       E1004: White space required before and after '-' at "-0o36" ~

White space in an expression is often required to make sure it is easy to read
and avoid errors.  Such as thinking that the "-0o36" above makes the number
negative, while it is actually seen as a subtraction.

To actually have the minus sign be used for negation, you can put the second
expression in parentheses: >

        echo -0x7f (-0o36)
<       -127 -30 ~

==============================================================================
*41.2*  Variables

A variable name consists of ASCII letters, digits and the underscore.  It
cannot start with a digit.  Valid variable names are:

        counter
        _aap3
        very_long_variable_name_with_underscores
        CamelCaseName
        LENGTH

Invalid names are "foo.bar" and "6var".

Some variables are global.  To see a list of currently defined global
variables type this command: >

        :let

You can use global variables everywhere.  However, it is too easy to use the
same name in two unrelated scripts.  Therefore variables declared in a script
are local to that script.  For example, if you have this in "script1.vim": >

        vim9script
        var counter = 5
        echo counter
<       5 ~

And you try to use the variable in "script2.vim": >

        vim9script
        echo counter
<       E121: Undefined variable: counter ~

Using a script-local variable means you can be sure that it is only changed in
that script and not elsewhere.

If you do want to share variables between scripts, use the "g:" prefix and
assign the value directly, do not use `var`.  And use a specific name to avoid
mistakes.  Thus in "script1.vim": >

        vim9script
        g:mash_counter = 5
        echo g:mash_counter
<       5 ~

And then in "script2.vim": >

        vim9script
        echo g:mash_counter
<       5 ~

Global variables can also be accessed on the command line, E.g. typing this: >
        echo g:mash_counter
That will not work for a script-local variable.

More about script-local variables here: |script-variable|.

There are more kinds of variables, see |internal-variables|.  The most often
used ones are:

        b:name          variable local to a buffer
        w:name          variable local to a window
        g:name          global variable (also in a function)
        v:name          variable predefined by Vim


DELETING VARIABLES

Variables take up memory and show up in the output of the `let` command.  To
delete a global variable use the `unlet` command.  Example: >

        unlet g:counter

This deletes the global variable "g:counter" to free up the memory it uses.
If you are not sure if the variable exists, and don't want an error message
when it doesn't, append !: >

        unlet! g:counter

You cannot `unlet` script-local variables in |Vim9| script, only in legacy
script.

When a script has been processed to the end, the local variables declared
there will not be deleted.  Functions defined in the script can use them.
Example:
>
        vim9script
        var counter = 0
        def g:GetCount(): number
          counter += 1
          return counter
        enddef

Every time you call the function it will return the next count: >
        :echo g:GetCount()
<       1 ~
>
        :echo g:GetCount()
<       2 ~

If you are worried a script-local variable is consuming too much memory, set
it to an empty or null value after you no longer need it.  Example: >
        var lines = readfile(...)
        ...
        lines = []

Note: below we'll leave out the `vim9script` line from examples, so we can
concentrate on the relevant commands, but you'll still need to put it at the
top of your script file.


STRING VARIABLES AND CONSTANTS

So far only numbers were used for the variable value.  Strings can be used as
well.  Numbers and strings are the basic types of variables that Vim supports.
Example: >

        var name = "Peter"
        echo name
<       Peter ~

Every variable has a type.  Very often, as in this example, the type is
defined by assigning a value.  This is called type inference.  If you do not
want to give the variable a value yet, you need to specify the type: >

        var name: string
        var age: number
        if male
           name = "Peter"
           age = 42
        else
           name = "Elisa"
           age = 45
        endif

If you make a mistake and try to assign the wrong type of value you'll get an
error: >

        age = "Peter"
<       E1012: Type mismatch; expected number but got string ~

More about types in |41.8|.

To assign a string value to a variable, you can use a string constant.  There
are two types of these.  First the string in double quotes, as we used
already.  If you want to include a double quote inside the string, put a
backslash in front of it: >

        var name = "he is \"Peter\""
        echo name
<       he is "Peter" ~

To avoid the need for backslashes, you can use a string in single quotes: >

        var name = 'he is "Peter"'
        echo name
<       he is "Peter" ~

Inside a single-quote string all the characters are as they are.  Only the
single quote itself is special: you need to use two to get one.  A backslash
is taken literally, thus you can't use it to change the meaning of the
character after it: >

        var name = 'P\e''ter'''
        echo name
<       P\e'ter' ~

In double-quote strings it is possible to use special characters.  Here are a
few useful ones:

        \t              <Tab>
        \n              <NL>, line break
        \r              <CR>, <Enter>
        \e              <Esc>
        \b              <BS>, backspace
        \"              "
        \\              \, backslash
        \<Esc>          <Esc>
        \<C-W>          CTRL-W

The last two are just examples.  The  "\<name>" form can be used to include
the special key "name".

See |expr-quote| for the full list of special items in a string.

==============================================================================
*41.3*  Expressions

Vim has a fairly standard way to handle expressions.  You can read the
definition here: |expression-syntax|.  Here we will show the most common
items.

The numbers, strings and variables mentioned above are expressions by
themselves.  Thus everywhere an expression is expected, you can use a number,
string or variable.  Other basic items in an expression are:

        $NAME           environment variable
        &name           option value
        @r              register contents

Examples: >

        echo "The value of 'tabstop' is" &ts
        echo "Your home directory is" $HOME
        if @a == 'text'

The &name form can also be used to set an option value, do something and
restore the old value.  Example: >

        var save_ic = &ic
        set noic
        s/The Start/The Beginning/
        &ic = save_ic

This makes sure the "The Start" pattern is used with the 'ignorecase' option
off.  Still, it keeps the value that the user had set.  (Another way to do
this would be to add "\C" to the pattern, see |/\C|.)


MATHEMATICS

It becomes more interesting if we combine these basic items.  Let's start with
mathematics on numbers:

        a + b           add
        a - b           subtract
        a * b           multiply
        a / b           divide
        a % b           modulo

The usual precedence is used.  Example: >

        echo 10 + 5 * 2
<       20 ~

Grouping is done with parentheses.  No surprises here.  Example: >

        echo (10 + 5) * 2
<       30 ~


OTHERS

Strings can be concatenated with ".." (see |expr6|).  Example: >

        echo "Name: " .. name
        Name: Peter

When the "echo" command gets multiple arguments, it separates them with a
space.  In the example the argument is a single expression, thus no space is
inserted.

If you don't like the concatenation you can use the $"string" form, which
accepts an expression in curly braces: >
        echo $"Name: {name}"

See |interpolated-string| for more information.

Borrowed from the C language is the conditional expression: >

        a ? b : c

If "a" evaluates to true "b" is used, otherwise "c" is used.  Example: >

        var nr = 4
        echo nr > 5 ? "nr is big" : "nr is small"
<       nr is small ~

The three parts of the constructs are always evaluated first, thus you could
see it works as: >

        (a) ? (b) : (c)

There is also the falsy operator: >
        echo name ?? "No name given"
See |??|.

==============================================================================
*41.4*  Conditionals

The `if` commands executes the following statements, until the matching
`endif`, only when a condition is met.  The generic form is:

        if {condition}
           {statements}
        endif

Only when the expression {condition} evaluates to true or one will the
{statements} be executed.  If they are not executed they must still be valid
commands.  If they contain garbage, Vim won't be able to find the matching
`endif`.

You can also use `else`.  The generic form for this is:

        if {condition}
           {statements}
        else
           {statements}
        endif

The second {statements} block is only executed if the first one isn't.

Finally, there is `elseif`

        if {condition}
           {statements}
        elseif {condition}
           {statements}
        endif

This works just like using `else` and then `if`, but without the need for an
extra `endif`.

A useful example for your vimrc file is checking the 'term' option and doing
something depending upon its value: >

        if &term == "xterm"
          # Do stuff for xterm
        elseif &term == "vt100"
          # Do stuff for a vt100 terminal
        else
          # Do something for other terminals
        endif

This uses "#" to start a comment, more about that later.


LOGIC OPERATIONS

We already used some of them in the examples.  These are the most often used
ones:

        a == b          equal to
        a != b          not equal to
        a >  b          greater than
        a >= b          greater than or equal to
        a <  b          less than
        a <= b          less than or equal to

The result is true if the condition is met and false otherwise.  An example: >

        if v:version >= 800
          echo "congratulations"
        else
          echo "you are using an old version, upgrade!"
        endif

Here "v:version" is a variable defined by Vim, which has the value of the Vim
version.  800 is for version 8.0, version 8.1 has the value 801.  This is
useful to write a script that works with multiple versions of Vim.
See |v:version|.  You can also check for a specific feature with `has()` or a
specific patch, see |has-patch|.

The logic operators work both for numbers and strings.  When comparing two
strings, the mathematical difference is used.  This compares byte values,
which may not be right for some languages.

If you try to compare a string with a number you will get an error.

For strings there are two more useful items:

        str =~ pat              matches with
        str !~ pat              does not match with

The left item "str" is used as a string.  The right item "pat" is used as a
pattern, like what's used for searching.  Example: >

        if str =~ " "
          echo "str contains a space"
        endif
        if str !~ '\.$'
          echo "str does not end in a full stop"
        endif

Notice the use of a single-quote string for the pattern.  This is useful,
because patterns tend to contain many backslashes and backslashes need to be
doubled in a double-quote string.

The match is not anchored, if you want to match the whole string start with
"^" and end with "$".

The 'ignorecase' option is not used when comparing strings.  When you do want
to ignore case append "?".  Thus "==?" compares two strings to be equal while
ignoring case.  For the full table see |expr-==|.


MORE LOOPING

The `while` command was already mentioned.  Two more statements can be used in
between the `while` and the `endwhile`:

        continue                Jump back to the start of the while loop; the
                                loop continues.
        break                   Jump forward to the `endwhile`; the loop is
                                discontinued.

Example: >

        var counter = 1
        while counter < 40
          if skip_number(counter)
            continue
          endif
          if last_number(counter)
            break
          endif
          sleep 50m
          ++counter
        endwhile

The `sleep` command makes Vim take a nap.  The "50m" specifies fifty
milliseconds.  Another example is `sleep 4`, which sleeps for four seconds.

`continue` and `break` can also be used in between `for` and `endfor`.
Even more looping can be done with the `for` command, see below in |41.8|.

==============================================================================
*41.5*  Executing an expression

So far the commands in the script were executed by Vim directly.  The
`execute` command allows executing the result of an expression.  This is a
very powerful way to build commands and execute them.

An example is to jump to a tag, which is contained in a variable: >

        execute "tag " .. tag_name

The ".." is used to concatenate the string "tag " with the value of variable
"tag_name".  Suppose "tag_name" has the value "get_cmd", then the command that
will be executed is: >

        tag get_cmd

The `execute` command can only execute Ex commands.  The `normal` command
executes Normal mode commands.  However, its argument is not an expression but
the literal command characters.  Example: >

        normal gg=G

This jumps to the first line with "gg" and formats all lines with the "="
operator and the "G" movement.

To make `normal` work with an expression, combine `execute` with it.
Example: >

        execute "normal " .. count .. "j"

This will move the cursor "count" lines down.

Make sure that the argument for `normal` is a complete command.  Otherwise
Vim will run into the end of the argument and silently abort the command.  For
example, if you start the delete operator, you must give the movement command
also.  This works: >

        normal d$

This does nothing: >

        normal d

If you start Insert mode and do not end it with Esc, it will end anyway.  This
works to insert "new text": >

        execute "normal inew text"

If you want to do something after inserting text you do need to end Insert
mode: >

        execute "normal inew text\<Esc>b"

This inserts "new text" and puts the cursor on the first letter of "text".
Notice the use of the special key "\<Esc>".  This avoids having to enter a
real <Esc> character in your script.  That is where `execute` with a
double-quote string comes in handy.

If you don't want to execute a string as a command but evaluate it to get the
result of the expression, you can use the eval() function: >

        var optname = "path"
        var optvalue = eval('&' .. optname)

A "&" character is prepended to "path", thus the argument to eval() is
"&path".  The result will then be the value of the 'path' option.

==============================================================================
*41.6*  Using functions

Vim defines many functions and provides a large amount of functionality that
way.  A few examples will be given in this section.  You can find the whole
list below: |function-list|.

A function is called with the parameters in between parentheses, separated by
commas.  Example: >

        search("Date: ", "W")

This calls the search() function, with arguments "Date: " and "W".  The
search() function uses its first argument as a search pattern and the second
one as flags.  The "W" flag means the search doesn't wrap around the end of
the file.

Using the `call` command is optional in |Vim9| script.  It is required in
legacy script and on the command line: >

        call search("Date: ", "W")

A function can be called in an expression.  Example: >

        var line = getline(".")
        var repl = substitute(line, '\a', "*", "g")
        setline(".", repl)

The getline() function obtains a line from the current buffer.  Its argument
is a specification of the line number.  In this case "." is used, which means
the line where the cursor is.

The substitute() function does something similar to the `:substitute` command.
The first argument "line" is the string on which to perform the substitution.
The second argument '\a' is the pattern, the third "*" is the replacement
string.  Finally, the last argument "g" is the flags.

The setline() function sets the line, specified by the first argument, to a
new string, the second argument.  In this example the line under the cursor is
replaced with the result of the substitute().  Thus the effect of the three
statements is equal to: >

        :substitute/\a/*/g

Using the functions becomes interesting when you do more work before and
after the substitute() call.


FUNCTIONS                                               *function-list*

There are many functions.  We will mention them here, grouped by what they are
used for.  You can find an alphabetical list here: |builtin-function-list|.
Use CTRL-] on the function name to jump to detailed help on it.

String manipulation:                                    *string-functions*
        nr2char()               get a character by its number value
        list2str()              get a character string from a list of numbers
        char2nr()               get number value of a character
        str2list()              get list of numbers from a string
        str2nr()                convert a string to a Number
        str2float()             convert a string to a Float
        printf()                format a string according to % items
        escape()                escape characters in a string with a '\'
        shellescape()           escape a string for use with a shell command
        fnameescape()           escape a file name for use with a Vim command
        tr()                    translate characters from one set to another
        strtrans()              translate a string to make it printable
        keytrans()              translate internal keycodes to a form that
                                can be used by |:map|
        tolower()               turn a string to lowercase
        toupper()               turn a string to uppercase
        charclass()             class of a character
        match()                 position where a pattern matches in a string
        matchend()              position where a pattern match ends in a string
        matchfuzzy()            fuzzy matches a string in a list of strings
        matchfuzzypos()         fuzzy matches a string in a list of strings
        matchstr()              match of a pattern in a string
        matchstrpos()           match and positions of a pattern in a string
        matchlist()             like matchstr() and also return submatches
        stridx()                first index of a short string in a long string
        strridx()               last index of a short string in a long string
        strlen()                length of a string in bytes
        strcharlen()            length of a string in characters
        strchars()              number of characters in a string
        strwidth()              size of string when displayed
        strdisplaywidth()       size of string when displayed, deals with tabs
        setcellwidths()         set character cell width overrides
        getcellwidths()         get character cell width overrides
        substitute()            substitute a pattern match with a string
        submatch()              get a specific match in ":s" and substitute()
        strpart()               get part of a string using byte index
        strcharpart()           get part of a string using char index
        slice()                 take a slice of a string, using char index in
                                Vim9 script
        strgetchar()            get character from a string using char index
        expand()                expand special keywords
        expandcmd()             expand a command like done for `:edit`
        iconv()                 convert text from one encoding to another
        byteidx()               byte index of a character in a string
        byteidxcomp()           like byteidx() but count composing characters
        charidx()               character index of a byte in a string
        repeat()                repeat a string multiple times
        eval()                  evaluate a string expression
        execute()               execute an Ex command and get the output
        win_execute()           like execute() but in a specified window
        trim()                  trim characters from a string
        gettext()               lookup message translation

List manipulation:                                      *list-functions*
        get()                   get an item without error for wrong index
        len()                   number of items in a List
        empty()                 check if List is empty
        insert()                insert an item somewhere in a List
        add()                   append an item to a List
        extend()                append a List to a List
        extendnew()             make a new List and append items
        remove()                remove one or more items from a List
        copy()                  make a shallow copy of a List
        deepcopy()              make a full copy of a List
        filter()                remove selected items from a List
        map()                   change each List item
        mapnew()                make a new List with changed items
        reduce()                reduce a List to a value
        slice()                 take a slice of a List
        sort()                  sort a List
        reverse()               reverse the order of a List or Blob
        uniq()                  remove copies of repeated adjacent items
        split()                 split a String into a List
        join()                  join List items into a String
        range()                 return a List with a sequence of numbers
        string()                String representation of a List
        call()                  call a function with List as arguments
        index()                 index of a value in a List or Blob
        indexof()               index in a List or Blob where an expression
                                evaluates to true
        max()                   maximum value in a List
        min()                   minimum value in a List
        count()                 count number of times a value appears in a List
        repeat()                repeat a List multiple times
        flatten()               flatten a List
        flattennew()            flatten a copy of a List

Dictionary manipulation:                                *dict-functions*
        get()                   get an entry without an error for a wrong key
        len()                   number of entries in a Dictionary
        has_key()               check whether a key appears in a Dictionary
        empty()                 check if Dictionary is empty
        remove()                remove an entry from a Dictionary
        extend()                add entries from one Dictionary to another
        extendnew()             make a new Dictionary and append items
        filter()                remove selected entries from a Dictionary
        map()                   change each Dictionary entry
        mapnew()                make a new Dictionary with changed items
        keys()                  get List of Dictionary keys
        values()                get List of Dictionary values
        items()                 get List of Dictionary key-value pairs
        copy()                  make a shallow copy of a Dictionary
        deepcopy()              make a full copy of a Dictionary
        string()                String representation of a Dictionary
        max()                   maximum value in a Dictionary
        min()                   minimum value in a Dictionary
        count()                 count number of times a value appears

Floating point computation:                             *float-functions*
        float2nr()              convert Float to Number
        abs()                   absolute value (also works for Number)
        round()                 round off
        ceil()                  round up
        floor()                 round down
        trunc()                 remove value after decimal point
        fmod()                  remainder of division
        exp()                   exponential
        log()                   natural logarithm (logarithm to base e)
        log10()                 logarithm to base 10
        pow()                   value of x to the exponent y
        sqrt()                  square root
        sin()                   sine
        cos()                   cosine
        tan()                   tangent
        asin()                  arc sine
        acos()                  arc cosine
        atan()                  arc tangent
        atan2()                 arc tangent
        sinh()                  hyperbolic sine
        cosh()                  hyperbolic cosine
        tanh()                  hyperbolic tangent
        isinf()                 check for infinity
        isnan()                 check for not a number

Blob manipulation:                                      *blob-functions*
        blob2list()             get a list of numbers from a blob
        list2blob()             get a blob from a list of numbers

Other computation:                                      *bitwise-function*
        and()                   bitwise AND
        invert()                bitwise invert
        or()                    bitwise OR
        xor()                   bitwise XOR
        sha256()                SHA-256 hash
        rand()                  get a pseudo-random number
        srand()                 initialize seed used by rand()

Variables:                                              *var-functions*
        type()                  type of a variable as a number
        typename()              type of a variable as text
        islocked()              check if a variable is locked
        funcref()               get a Funcref for a function reference
        function()              get a Funcref for a function name
        getbufvar()             get a variable value from a specific buffer
        setbufvar()             set a variable in a specific buffer
        getwinvar()             get a variable from specific window
        gettabvar()             get a variable from specific tab page
        gettabwinvar()          get a variable from specific window & tab page
        setwinvar()             set a variable in a specific window
        settabvar()             set a variable in a specific tab page
        settabwinvar()          set a variable in a specific window & tab page
        garbagecollect()        possibly free memory

Cursor and mark position:               *cursor-functions* *mark-functions*
        col()                   column number of the cursor or a mark
        virtcol()               screen column of the cursor or a mark
        line()                  line number of the cursor or mark
        wincol()                window column number of the cursor
        winline()               window line number of the cursor
        cursor()                position the cursor at a line/column
        screencol()             get screen column of the cursor
        screenrow()             get screen row of the cursor
        screenpos()             screen row and col of a text character
        virtcol2col()           byte index of a text character on screen
        getcurpos()             get position of the cursor
        getpos()                get position of cursor, mark, etc.
        setpos()                set position of cursor, mark, etc.
        getmarklist()           list of global/local marks
        byte2line()             get line number at a specific byte count
        line2byte()             byte count at a specific line
        diff_filler()           get the number of filler lines above a line
        screenattr()            get attribute at a screen line/row
        screenchar()            get character code at a screen line/row
        screenchars()           get character codes at a screen line/row
        screenstring()          get string of characters at a screen line/row
        charcol()               character number of the cursor or a mark
        getcharpos()            get character position of cursor, mark, etc.
        setcharpos()            set character position of cursor, mark, etc.
        getcursorcharpos()      get character position of the cursor
        setcursorcharpos()      set character position of the cursor

Working with text in the current buffer:                *text-functions*
        getline()               get a line or list of lines from the buffer
        setline()               replace a line in the buffer
        append()                append line or list of lines in the buffer
        indent()                indent of a specific line
        cindent()               indent according to C indenting
        lispindent()            indent according to Lisp indenting
        nextnonblank()          find next non-blank line
        prevnonblank()          find previous non-blank line
        search()                find a match for a pattern
        searchpos()             find a match for a pattern
        searchcount()           get number of matches before/after the cursor
        searchpair()            find the other end of a start/skip/end
        searchpairpos()         find the other end of a start/skip/end
        searchdecl()            search for the declaration of a name
        getcharsearch()         return character search information
        setcharsearch()         set character search information

Working with text in another buffer:
        getbufline()            get a list of lines from the specified buffer
        getbufoneline()         get a one line from the specified buffer
        setbufline()            replace a line in the specified buffer
        appendbufline()         append a list of lines in the specified buffer
        deletebufline()         delete lines from a specified buffer

                                        *system-functions* *file-functions*
System functions and manipulation of files:
        glob()                  expand wildcards
        globpath()              expand wildcards in a number of directories
        glob2regpat()           convert a glob pattern into a search pattern
        findfile()              find a file in a list of directories
        finddir()               find a directory in a list of directories
        resolve()               find out where a shortcut points to
        fnamemodify()           modify a file name
        pathshorten()           shorten directory names in a path
        simplify()              simplify a path without changing its meaning
        executable()            check if an executable program exists
        exepath()               full path of an executable program
        filereadable()          check if a file can be read
        filewritable()          check if a file can be written to
        getfperm()              get the permissions of a file
        setfperm()              set the permissions of a file
        getftype()              get the kind of a file
        isabsolutepath()        check if a path is absolute
        isdirectory()           check if a directory exists
        getfsize()              get the size of a file
        getcwd()                get the current working directory
        haslocaldir()           check if current window used |:lcd| or |:tcd|
        tempname()              get the name of a temporary file
        mkdir()                 create a new directory
        chdir()                 change current working directory
        delete()                delete a file
        rename()                rename a file
        system()                get the result of a shell command as a string
        systemlist()            get the result of a shell command as a list
        environ()               get all environment variables
        getenv()                get one environment variable
        setenv()                set an environment variable
        hostname()              name of the system
        readfile()              read a file into a List of lines
        readblob()              read a file into a Blob
        readdir()               get a List of file names in a directory
        readdirex()             get a List of file information in a directory
        writefile()             write a List of lines or Blob into a file

Date and Time:                          *date-functions* *time-functions*
        getftime()              get last modification time of a file
        localtime()             get current time in seconds
        strftime()              convert time to a string
        strptime()              convert a date/time string to time
        reltime()               get the current or elapsed time accurately
        reltimestr()            convert reltime() result to a string
        reltimefloat()          convert reltime() result to a Float

Autocmds:                                       *autocmd-functions*
        autocmd_add()           add a list of autocmds and groups
        autocmd_delete()        delete a list of autocmds and groups
        autocmd_get()           return a list of autocmds

                        *buffer-functions* *window-functions* *arg-functions*
Buffers, windows and the argument list:
        argc()                  number of entries in the argument list
        argidx()                current position in the argument list
        arglistid()             get id of the argument list
        argv()                  get one entry from the argument list
        bufadd()                add a file to the list of buffers
        bufexists()             check if a buffer exists
        buflisted()             check if a buffer exists and is listed
        bufload()               ensure a buffer is loaded
        bufloaded()             check if a buffer exists and is loaded
        bufname()               get the name of a specific buffer
        bufnr()                 get the buffer number of a specific buffer
        tabpagebuflist()        return List of buffers in a tab page
        tabpagenr()             get the number of a tab page
        tabpagewinnr()          like winnr() for a specified tab page
        winnr()                 get the window number for the current window
        bufwinid()              get the window ID of a specific buffer
        bufwinnr()              get the window number of a specific buffer
        winbufnr()              get the buffer number of a specific window
        listener_add()          add a callback to listen to changes
        listener_flush()        invoke listener callbacks
        listener_remove()       remove a listener callback
        win_findbuf()           find windows containing a buffer
        win_getid()             get window ID of a window
        win_gettype()           get type of window
        win_gotoid()            go to window with ID
        win_id2tabwin()         get tab and window nr from window ID
        win_id2win()            get window nr from window ID
        win_move_separator()    move window vertical separator
        win_move_statusline()   move window status line
        win_splitmove()         move window to a split of another window
        getbufinfo()            get a list with buffer information
        gettabinfo()            get a list with tab page information
        getwininfo()            get a list with window information
        getchangelist()         get a list of change list entries
        getjumplist()           get a list of jump list entries
        swapfilelist()          list of existing swap files in 'directory'
        swapinfo()              information about a swap file
        swapname()              get the swap file path of a buffer

Command line:                                   *command-line-functions*
        getcmdcompltype()       get the type of the current command line
                                completion
        getcmdline()            get the current command line
        getcmdpos()             get position of the cursor in the command line
        getcmdscreenpos()       get screen position of the cursor in the
                                command line
        setcmdline()            set the current command line
        setcmdpos()             set position of the cursor in the command line
        getcmdtype()            return the current command-line type
        getcmdwintype()         return the current command-line window type
        getcompletion()         list of command-line completion matches
        fullcommand()           get full command name

Quickfix and location lists:                    *quickfix-functions*
        getqflist()             list of quickfix errors
        setqflist()             modify a quickfix list
        getloclist()            list of location list items
        setloclist()            modify a location list

Insert mode completion:                         *completion-functions*
        complete()              set found matches
        complete_add()          add to found matches
        complete_check()        check if completion should be aborted
        complete_info()         get current completion information
        pumvisible()            check if the popup menu is displayed
        pum_getpos()            position and size of popup menu if visible

Folding:                                        *folding-functions*
        foldclosed()            check for a closed fold at a specific line
        foldclosedend()         like foldclosed() but return the last line
        foldlevel()             check for the fold level at a specific line
        foldtext()              generate the line displayed for a closed fold
        foldtextresult()        get the text displayed for a closed fold

Syntax and highlighting:          *syntax-functions* *highlighting-functions*
        clearmatches()          clear all matches defined by |matchadd()| and
                                the |:match| commands
        getmatches()            get all matches defined by |matchadd()| and
                                the |:match| commands
        hlexists()              check if a highlight group exists
        hlget()                 get highlight group attributes
        hlset()                 set highlight group attributes
        hlID()                  get ID of a highlight group
        synID()                 get syntax ID at a specific position
        synIDattr()             get a specific attribute of a syntax ID
        synIDtrans()            get translated syntax ID
        synstack()              get list of syntax IDs at a specific position
        synconcealed()          get info about concealing
        diff_hlID()             get highlight ID for diff mode at a position
        matchadd()              define a pattern to highlight (a "match")
        matchaddpos()           define a list of positions to highlight
        matcharg()              get info about |:match| arguments
        matchdelete()           delete a match defined by |matchadd()| or a
                                |:match| command
        setmatches()            restore a list of matches saved by
                                |getmatches()|

Spelling:                                       *spell-functions*
        spellbadword()          locate badly spelled word at or after cursor
        spellsuggest()          return suggested spelling corrections
        soundfold()             return the sound-a-like equivalent of a word

History:                                        *history-functions*
        histadd()               add an item to a history
        histdel()               delete an item from a history
        histget()               get an item from a history
        histnr()                get highest index of a history list

Interactive:                                    *interactive-functions*
        browse()                put up a file requester
        browsedir()             put up a directory requester
        confirm()               let the user make a choice
        getchar()               get a character from the user
        getcharstr()            get a character from the user as a string
        getcharmod()            get modifiers for the last typed character
        getmousepos()           get last known mouse position
        getmouseshape()         get name of the current mouse shape
        echoraw()               output characters as-is
        feedkeys()              put characters in the typeahead queue
        input()                 get a line from the user
        inputlist()             let the user pick an entry from a list
        inputsecret()           get a line from the user without showing it
        inputdialog()           get a line from the user in a dialog
        inputsave()             save and clear typeahead
        inputrestore()          restore typeahead

GUI:                                            *gui-functions*
        getfontname()           get name of current font being used
        getwinpos()             position of the Vim window
        getwinposx()            X position of the Vim window
        getwinposy()            Y position of the Vim window
        balloon_show()          set the balloon content
        balloon_split()         split a message for a balloon
        balloon_gettext()       get the text in the balloon

Vim server:                                     *server-functions*
        serverlist()            return the list of server names
        remote_startserver()    run a server
        remote_send()           send command characters to a Vim server
        remote_expr()           evaluate an expression in a Vim server
        server2client()         send a reply to a client of a Vim server
        remote_peek()           check if there is a reply from a Vim server
        remote_read()           read a reply from a Vim server
        foreground()            move the Vim window to the foreground
        remote_foreground()     move the Vim server window to the foreground

Window size and position:                       *window-size-functions*
        winheight()             get height of a specific window
        winwidth()              get width of a specific window
        win_screenpos()         get screen position of a window
        winlayout()             get layout of windows in a tab page
        winrestcmd()            return command to restore window sizes
        winsaveview()           get view of current window
        winrestview()           restore saved view of current window

Mappings and Menus:                         *mapping-functions*
        digraph_get()           get |digraph|
        digraph_getlist()       get all |digraph|s
        digraph_set()           register |digraph|
        digraph_setlist()       register multiple |digraph|s
        hasmapto()              check if a mapping exists
        mapcheck()              check if a matching mapping exists
        maparg()                get rhs of a mapping
        maplist()               get list of all mappings
        mapset()                restore a mapping
        menu_info()             get information about a menu item
        wildmenumode()          check if the wildmode is active

Testing:                                    *test-functions*
        assert_equal()          assert that two expressions values are equal
        assert_equalfile()      assert that two file contents are equal
        assert_notequal()       assert that two expressions values are not equal
        assert_inrange()        assert that an expression is inside a range
        assert_match()          assert that a pattern matches the value
        assert_notmatch()       assert that a pattern does not match the value
        assert_false()          assert that an expression is false
        assert_true()           assert that an expression is true
        assert_exception()      assert that a command throws an exception
        assert_beeps()          assert that a command beeps
        assert_nobeep()         assert that a command does not cause a beep
        assert_fails()          assert that a command fails
        assert_report()         report a test failure
        test_alloc_fail()       make memory allocation fail
        test_autochdir()        enable 'autochdir' during startup
        test_override()         test with Vim internal overrides
        test_garbagecollect_now()   free memory right now
        test_garbagecollect_soon()  set a flag to free memory soon
        test_getvalue()         get value of an internal variable
        test_gui_event()        generate a GUI event for testing
        test_ignore_error()     ignore a specific error message
        test_mswin_event()      generate an MS-Windows event
        test_null_blob()        return a null Blob
        test_null_channel()     return a null Channel
        test_null_dict()        return a null Dict
        test_null_function()    return a null Funcref
        test_null_job()         return a null Job
        test_null_list()        return a null List
        test_null_partial()     return a null Partial function
        test_null_string()      return a null String
        test_settime()          set the time Vim uses internally
        test_setmouse()         set the mouse position
        test_feedinput()        add key sequence to input buffer
        test_option_not_set()   reset flag indicating option was set
        test_refcount()         return an expression's reference count
        test_srand_seed()       set the seed value for srand()
        test_unknown()          return a value with unknown type
        test_void()             return a value with void type

Inter-process communication:                *channel-functions*
        ch_canread()            check if there is something to read
        ch_open()               open a channel
        ch_close()              close a channel
        ch_close_in()           close the in part of a channel
        ch_read()               read a message from a channel
        ch_readblob()           read a Blob from a channel
        ch_readraw()            read a raw message from a channel
        ch_sendexpr()           send a JSON message over a channel
        ch_sendraw()            send a raw message over a channel
        ch_evalexpr()           evaluate an expression over channel
        ch_evalraw()            evaluate a raw string over channel
        ch_status()             get status of a channel
        ch_getbufnr()           get the buffer number of a channel
        ch_getjob()             get the job associated with a channel
        ch_info()               get channel information
        ch_log()                write a message in the channel log file
        ch_logfile()            set the channel log file
        ch_setoptions()         set the options for a channel
        json_encode()           encode an expression to a JSON string
        json_decode()           decode a JSON string to Vim types
        js_encode()             encode an expression to a JSON string
        js_decode()             decode a JSON string to Vim types

Jobs:                                           *job-functions*
        job_start()             start a job
        job_stop()              stop a job
        job_status()            get the status of a job
        job_getchannel()        get the channel used by a job
        job_info()              get information about a job
        job_setoptions()        set options for a job

Signs:                                          *sign-functions*
        sign_define()           define or update a sign
        sign_getdefined()       get a list of defined signs
        sign_getplaced()        get a list of placed signs
        sign_jump()             jump to a sign
        sign_place()            place a sign
        sign_placelist()        place a list of signs
        sign_undefine()         undefine a sign
        sign_unplace()          unplace a sign
        sign_unplacelist()      unplace a list of signs

Terminal window:                                *terminal-functions*
        term_start()            open a terminal window and run a job
        term_list()             get the list of terminal buffers
        term_sendkeys()         send keystrokes to a terminal
        term_wait()             wait for screen to be updated
        term_getjob()           get the job associated with a terminal
        term_scrape()           get row of a terminal screen
        term_getline()          get a line of text from a terminal
        term_getattr()          get the value of attribute {what}
        term_getcursor()        get the cursor position of a terminal
        term_getscrolled()      get the scroll count of a terminal
        term_getaltscreen()     get the alternate screen flag
        term_getsize()          get the size of a terminal
        term_getstatus()        get the status of a terminal
        term_gettitle()         get the title of a terminal
        term_gettty()           get the tty name of a terminal
        term_setansicolors()    set 16 ANSI colors, used for GUI
        term_getansicolors()    get 16 ANSI colors, used for GUI
        term_dumpdiff()         display difference between two screen dumps
        term_dumpload()         load a terminal screen dump in a window
        term_dumpwrite()        dump contents of a terminal screen to a file
        term_setkill()          set signal to stop job in a terminal
        term_setrestore()       set command to restore a terminal
        term_setsize()          set the size of a terminal
        term_setapi()           set terminal JSON API function name prefix

Popup window:                                   *popup-window-functions*
        popup_create()          create popup centered in the screen
        popup_atcursor()        create popup just above the cursor position,
                                closes when the cursor moves away
        popup_beval()           at the position indicated by v:beval_
                                variables, closes when the mouse moves away
        popup_notification()    show a notification for three seconds
        popup_dialog()          create popup centered with padding and border
        popup_menu()            prompt for selecting an item from a list
        popup_hide()            hide a popup temporarily
        popup_show()            show a previously hidden popup
        popup_move()            change the position and size of a popup
        popup_setoptions()      override options of a popup
        popup_settext()         replace the popup buffer contents
        popup_close()           close one popup
        popup_clear()           close all popups
        popup_filter_menu()     select from a list of items
        popup_filter_yesno()    block until 'y' or 'n' is pressed
        popup_getoptions()      get current options for a popup
        popup_getpos()          get actual position and size of a popup
        popup_findecho()        get window ID for popup used for `:echowindow`
        popup_findinfo()        get window ID for popup info window
        popup_findpreview()     get window ID for popup preview window
        popup_list()            get list of all popup window IDs
        popup_locate()          get popup window ID from its screen position

Timers:                                         *timer-functions*
        timer_start()           create a timer
        timer_pause()           pause or unpause a timer
        timer_stop()            stop a timer
        timer_stopall()         stop all timers
        timer_info()            get information about timers

Tags:                                           *tag-functions*
        taglist()               get list of matching tags
        tagfiles()              get a list of tags files
        gettagstack()           get the tag stack of a window
        settagstack()           modify the tag stack of a window

Prompt Buffer:                                  *promptbuffer-functions*
        prompt_getprompt()      get the effective prompt text for a buffer
        prompt_setcallback()    set prompt callback for a buffer
        prompt_setinterrupt()   set interrupt callback for a buffer
        prompt_setprompt()      set the prompt text for a buffer

Registers:                                      *register-functions*
        getreg()                get contents of a register
        getreginfo()            get information about a register
        getregtype()            get type of a register
        setreg()                set contents and type of a register
        reg_executing()         return the name of the register being executed
        reg_recording()         return the name of the register being recorded

Text Properties:                                *text-property-functions*
        prop_add()              attach a property at a position
        prop_add_list()         attach a property at multiple positions
        prop_clear()            remove all properties from a line or lines
        prop_find()             search for a property
        prop_list()             return a list of all properties in a line
        prop_remove()           remove a property from a line
        prop_type_add()         add/define a property type
        prop_type_change()      change properties of a type
        prop_type_delete()      remove a text property type
        prop_type_get()         return the properties of a type
        prop_type_list()        return a list of all property types

Sound:                                                  *sound-functions*
        sound_clear()           stop playing all sounds
        sound_playevent()       play an event's sound
        sound_playfile()        play a sound file
        sound_stop()            stop playing a sound

Various:                                        *various-functions*
        mode()                  get current editing mode
        state()                 get current busy state
        visualmode()            last visual mode used
        exists()                check if a variable, function, etc. exists
        exists_compiled()       like exists() but check at compile time
        has()                   check if a feature is supported in Vim
        changenr()              return number of most recent change
        cscope_connection()     check if a cscope connection exists
        did_filetype()          check if a FileType autocommand was used
        eventhandler()          check if invoked by an event handler
        getpid()                get process ID of Vim
        getscriptinfo()         get list of sourced vim scripts
        getimstatus()           check if IME status is active
        interrupt()             interrupt script execution
        windowsversion()        get MS-Windows version
        terminalprops()         properties of the terminal

        libcall()               call a function in an external library
        libcallnr()             idem, returning a number

        undofile()              get the name of the undo file
        undotree()              return the state of the undo tree

        shiftwidth()            effective value of 'shiftwidth'

        wordcount()             get byte/word/char count of buffer

        luaeval()               evaluate |Lua| expression
        mzeval()                evaluate |MzScheme| expression
        perleval()              evaluate Perl expression (|+perl|)
        py3eval()               evaluate Python expression (|+python3|)
        pyeval()                evaluate Python expression (|+python|)
        pyxeval()               evaluate |python_x| expression
        rubyeval()              evaluate |Ruby| expression

        debugbreak()            interrupt a program being debugged

==============================================================================
*41.7*  Defining a function

Vim enables you to define your own functions.  The basic function declaration
begins as follows: >

        def {name}({var1}, {var2}, ...): return-type
          {body}
        enddef
<
        Note:
        Function names must begin with a capital letter.

Let's define a short function to return the smaller of two numbers.  It starts
with this line: >

        def Min(num1: number, num2: number): number

This tells Vim that the function is named "Min", it takes two arguments that
are numbers: "num1" and "num2" and returns a number.

The first thing you need to do is to check to see which number is smaller:
   >
        if num1 < num2

Let's assign the variable "smaller" the value of the smallest number: >

        var smaller: number
        if num1 < num2
          smaller = num1
        else
          smaller = num2
        endif

The variable "smaller" is a local variable.  It is declared to be a number,
that way Vim can warn you for any mistakes.  Variables used inside a function
are local unless prefixed by something like "g:", "w:", or "b:".

        Note:
        To access a global variable from inside a function you must prepend
        "g:" to it.  Thus "g:today" inside a function is used for the global
        variable "today", and "today" is another variable, local to the
        function or the script.

You now use the `return` statement to return the smallest number to the user.
Finally, you end the function: >

          return smaller
        enddef

The complete function definition is as follows: >

        def Min(num1: number, num2: number): number
          var smaller: number
          if num1 < num2
            smaller = num1
          else
            smaller = num2
          endif
          return smaller
        enddef

Obviously this is a verbose example.  You can make it shorter by using two
return commands: >

        def Min(num1: number, num2: number): number
          if num1 < num2
            return num1
          endif
          return num2
        enddef

And if you remember the conditional expression, you need only one line: >

        def Min(num1: number, num2: number): number
          return num1 < num2 ? num1 : num2
        enddef

A user defined function is called in exactly the same way as a built-in
function.  Only the name is different.  The Min function can be used like
this: >

        echo Min(5, 8)

Only now will the function be executed and the lines be parsed by Vim.
If there are mistakes, like using an undefined variable or function, you will
now get an error message.  When defining the function these errors are not
detected.  To get the errors sooner you can tell Vim to compile all the
functions in the script: >

        defcompile

Compiling functions takes a little time, but does report errors early.  You
could use `:defcompile` at the end of your script while working on it, and
comment it out when everything is fine.

For a function that does not return anything simply leave out the return type: >

        def SayIt(text: string)
          echo text
        enddef

If you want to return any kind of value, you can use the "any" return type: >
        def GetValue(): any
This disables type checking for the return value, use only when needed.

It is also possible to define a legacy function with `function` and
`endfunction`.  These do not have types and are not compiled.  Therefore they
execute much slower.


USING A RANGE

A line range can be used with a function call.  The function will be called
once for every line in the range, with the cursor in that line.  Example: >

        def Number()
          echo "line " .. line(".") .. " contains: " .. getline(".")
        enddef

If you call this function with: >

        :10,15Number()

The function will be called six times, starting on line 10 and ending on line
15.


LISTING FUNCTIONS

The `function` command lists the names and arguments of all user-defined
functions: >

        :function
<       def <SNR>86_Show(start: string, ...items: list<string>) ~
        function GetVimIndent() ~
        function SetSyn(name) ~

The "<SNR>" prefix means that a function is script-local.  |Vim9| functions
will start with "def" and include argument and return types.  Legacy functions
are listed with "function".

To see what a function does, use its name as an argument for `function`: >

        :function SetSyn
<       1     if &syntax == '' ~
        2       let &syntax = a:name ~
        3     endif ~
           endfunction ~

To see the "Show" function you need to include the script prefix, since
multiple "Show" functions can be defined in different scripts.  To find
the exact name you can use `function`, but the result may be a very long list.
To only get the functions matching a pattern you can use the `filter` prefix:
>
        :filter Show function
<       def <SNR>86_Show(start: string, ...items: list<string>) ~
>
        :function <SNR>86_Show
<       1    echohl Title ~
        2    echo "start is " .. start ~
        etc.


DEBUGGING

The line number is useful for when you get an error message or when debugging.
See |debug-scripts| about debugging mode.

You can also set the 'verbose' option to 12 or higher to see all function
calls.  Set it to 15 or higher to see every executed line.


DELETING A FUNCTION

To delete the SetSyn() function: >

        :delfunction SetSyn

Deleting only works for global functions and functions in legacy script, not
for functions defined in a |Vim9| script.

You get an error when the function doesn't exist or cannot be deleted.


FUNCTION REFERENCES

Sometimes it can be useful to have a variable point to one function or
another.  You can do it with a function reference variable.  Often shortened
to "funcref".  Example: >

        def Right(): string
          return 'Right!'
        enddef
        def Wrong(): string
          return 'Wrong!'
        enddef

        var Afunc = g:result == 1 ? Right : Wrong
        echo Afunc()
<       Wrong! ~

This assumes "g:result" is not one.  See |Funcref| for details.

Note that the name of a variable that holds a function reference must start
with a capital.  Otherwise it could be confused with the name of a builtin
function.


FURTHER READING

Using a variable number of arguments is introduced in section |50.2|.

More information about defining your own functions here: |user-functions|.

==============================================================================
*41.8*  Lists and Dictionaries

So far we have used the basic types String and Number.  Vim also supports two
composite types: List and Dictionary.

A List is an ordered sequence of items.  The items can be any kind of value,
thus you can make a List of numbers, a List of Lists and even a List of mixed
items.  To create a List with three strings: >

        var alist = ['aap', 'noot', 'mies']

The List items are enclosed in square brackets and separated by commas.  To
create an empty List: >

        var alist = []

You can add items to a List with the add() function: >

        var alist = []
        add(alist, 'foo')
        add(alist, 'bar')
        echo alist
<       ['foo', 'bar'] ~

List concatenation is done with +: >

        var alist = ['foo', 'bar']
        alist = alist + ['and', 'more']
        echo alist
<       ['foo', 'bar', 'and', 'more'] ~

Or, if you want to extend a List with a function, use `extend()`: >

        var alist = ['one']
        extend(alist, ['two', 'three'])
        echo alist
<       ['one', 'two', 'three'] ~

Notice that using `add()` will have a different effect than `extend()`: >

        var alist = ['one']
        add(alist, ['two', 'three'])
        echo alist
<       ['one', ['two', 'three']] ~

The second argument of add() is added as an item, now you have a nested list.


FOR LOOP

One of the nice things you can do with a List is iterate over it: >

        var alist = ['one', 'two', 'three']
        for n in alist
          echo n
        endfor
<       one ~
        two ~
        three ~

This will loop over each element in List "alist", assigning each value to
variable "n".  The generic form of a for loop is: >

        for {varname} in {list-expression}
          {commands}
        endfor

To loop a certain number of times you need a List of a specific length.  The
range() function creates one for you: >

        for a in range(3)
          echo a
        endfor
<       0 ~
        1 ~
        2 ~

Notice that the first item of the List that range() produces is zero, thus the
last item is one less than the length of the list.  Detail: Internally range()
does not actually create the list, so that a large range used in a for loop
works efficiently.  When used elsewhere, the range is turned into an actual
list, which takes more time for a long list.

You can also specify the maximum value, the stride and even go backwards: >

        for a in range(8, 4, -2)
          echo a
        endfor
<       8 ~
        6 ~
        4 ~

A more useful example, looping over all the lines in the buffer: >

        for line in getline(1, 50)
          if line =~ "Date: "
            echo line
          endif
        endfor

This looks into lines 1 to 50 (inclusive) and echoes any date found in there.

For further reading see |Lists|.


DICTIONARIES

A Dictionary stores key-value pairs.  You can quickly lookup a value if you
know the key.  A Dictionary is created with curly braces: >

        var uk2nl = {one: 'een', two: 'twee', three: 'drie'}

Now you can lookup words by putting the key in square brackets: >

        echo uk2nl['two']
<       twee ~

If the key does not have special characters, you can use the dot notation: >

        echo uk2nl.two
<       twee ~

The generic form for defining a Dictionary is: >

        {<key> : <value>, ...}

An empty Dictionary is one without any keys: >

        {}

The possibilities with Dictionaries are numerous.  There are various functions
for them as well.  For example, you can obtain a list of the keys and loop
over them: >

        for key in keys(uk2nl)
          echo key
        endfor
<       three ~
        one ~
        two ~

You will notice the keys are not ordered.  You can sort the list to get a
specific order: >

        for key in sort(keys(uk2nl))
          echo key
        endfor
<       one ~
        three ~
        two ~

But you can never get back the order in which items are defined.  For that you
need to use a List, it stores items in an ordered sequence.

For further reading see |Dictionaries|.

==============================================================================
*41.9*  White space

Blank lines are allowed in a script and ignored.

Leading whitespace characters (blanks and TABs) are ignored, except when using
|:let-heredoc| without "trim".

Trailing whitespace is often ignored, but not always.  One command that
includes it is `map`.  You have to watch out for that, it can cause hard to
understand mistakes.  A generic solution is to never use trailing white space,
unless you really need it.

To include a whitespace character in the value of an option, it must be
escaped by a "\" (backslash)  as in the following example: >

        :set tags=my\ nice\ file

If it would be written as: >

        :set tags=my nice file

This will issue an error, because it is interpreted as: >

        :set tags=my
        :set nice
        :set file

|Vim9| script is very picky when it comes to white space.  This was done
intentionally to make sure scripts are easy to read and to avoid mistakes.
If you use white space sensibly it will just work.  When not you will get an
error message telling you where white space is missing or should be removed.

==============================================================================
*41.10* Line continuation

In legacy Vim script line continuation is done by preceding a continuation
line with a backslash: >
        let mylist = [
                        \ 'one',
                        \ 'two',
                        \ ]

This requires the 'cpo' option to exclude the "C" flag.  Normally this is done
by putting this at the start of the script: >
        let s:save_cpo = &cpo
        set cpo&vim

And restore the option at the end of the script: >
        let &cpo = s:save_cpo
        unlet s:save_cpo

A few more details can be found here: |line-continuation|.

In |Vim9| script the backslash can still be used, but in most places it is not
needed: >
        var mylist = [
                        'one',
                        'two',
                        ]

Also, the 'cpo' option does not need to be changed.  See
|vim9-line-continuation| for details.

==============================================================================
*41.11* Comments

In |Vim9| script the character # starts a comment.  That character and
everything after it until the end-of-line is considered a comment and
is ignored, except for commands that don't consider comments, as shown in
examples below.  A comment can start on any character position on the line,
but not when it is part of the command, e.g. inside a string.

The character " (the double quote mark) starts a comment in legacy script.
This involves some cleverness to make sure double quoted strings are not
recognized as comments (just one reason to prefer |Vim9| script).

There is a little "catch" with comments for some commands.  Examples: >

        abbrev dev development  # shorthand
        map <F3> o#include      # insert include
        execute cmd             # do it
        !ls *.c                 # list C files

- The abbreviation 'dev' will be expanded to 'development  # shorthand'.
- The mapping of <F3> will actually be the whole line after the 'o# ....'
  including the '# insert include'.
- The `execute` command will give an error.
- The `!` command will send everything after it to the shell, most likely
  causing an error.

There can be no comment after `map`, `abbreviate`, `execute` and `!` commands
(there are a few more commands with this restriction).  For the `map`,
`abbreviate` and `execute` commands there is a trick: >

        abbrev dev development|# shorthand
        map <F3> o#include|# insert include
        execute '!ls *.c'       |# do it

With the '|' character the command is separated from the next one.  And that
next command is only a comment.  The last command, using `execute` is a
general solution, it works for all commands that do not accept a comment or a
'|' to separate the next command.

Notice that there is no white space before the '|' in the abbreviation and
mapping.  For these commands, any character until the end-of-line or '|' is
included.  As a consequence of this behavior, you don't always see that
trailing whitespace is included: >

        map <F4> o#include  

Here it is intended, in other cases it might be accidental.  To spot these
problems, you can highlight trailing spaces: >
        match Search /\s\+$/

For Unix there is one special way to comment a line, that allows making a Vim
script executable, and it also works in legacy script: >
        #!/usr/bin/env vim -S
        echo "this is a Vim script"
        quit

==============================================================================
*41.12* Fileformat

The end-of-line character depends on the system.  For Vim scripts it is
recommended to always use the Unix fileformat.  Lines are then separated with
the Newline character.  This also works on any other system.  That way you can
copy your Vim scripts from MS-Windows to Unix and they still work.  See
|:source_crnl|.  To be sure it is set right, do this before writing the file:
>
        :setlocal fileformat=unix

When using "dos" fileformat, lines are separated with CR-NL, two characters.
The CR character causes various problems, better avoid this.

==============================================================================

Advance information about writing Vim script is in |usr_50.txt|.

Next chapter: |usr_42.txt|  Add new menus

Copyright: see |manual-copyright|  vim:tw=78:ts=8:noet:ft=help:norl: