Usr_41

Nvim :help pages, generated from source using the tree-sitter-vimdoc parser.

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, thus 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 Exceptions 41.10 Various remarks 41.11 Writing a plugin 41.12 Writing a filetype plugin 41.13 Writing a compiler plugin 41.14 Writing a plugin that loads quickly 41.15 Writing library scripts 41.16 Distributing Vim scripts
Next chapter: usr_42.txt Add new menus Previous chapter: usr_40.txt Make new commands Table of contents: usr_toc.txt

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 values you prefer. And 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.
If you are familiar with Python, you can find a comparison between Python and Vim script here, with pointers to other documents: https://gist.github.com/yegappan/16d964a37ead0979b05e655aa036cad0 And if you are familiar with JavaScript: https://w0rp.com/blog/post/vim-script-for-the-javascripter/
Let's start with a simple example:
:let i = 1
:while i < 5
:  echo "count is" i
:  let i += 1
:endwhile
Note: The ":" characters are not really needed here. You only need to use them when you type a command. In a Vim script file they can be left out. We will use them here anyway to make clear these are colon commands and make them stand out from Normal mode commands. Note: You can try out the examples by yanking the lines from the text here and executing them with :@"
The output of the example code is:
count is 1
count is 2
count is 3
count is 4
In the first line the ":let" command assigns a value to a variable. The generic form is:
:let {variable} = {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 ":let i += 1" command. This does the same thing as ":let i = i + 1". This 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 and range() work until later. Follow the links if you are impatient.

FOUR KINDS OF NUMBERS

Numbers can be decimal, hexadecimal, octal or binary.
A hexadecimal number starts with "0x" or "0X". For example "0x1f" is decimal

31.

An octal number starts with "0o", "0O" or a zero and another digit. "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: don't put a zero before a decimal number, it will be interpreted as an octal number!
The ":echo" command always prints decimal numbers. Example:
:echo 0x7f 0o36
127 30
A number is made negative with a minus sign. This also works for hexadecimal, octal and binary numbers. A minus sign is also used for subtraction. Compare this with the previous example:
:echo 0x7f -0o36
97
White space in an expression is ignored. However, it's recommended to use it for separating items, to make the expression easier to read. For example, to avoid the confusion with a negative number above, put a space between the minus sign and the following number:
:echo 0x7f - 0o36

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 FuncLength LENGTH
Invalid names are "foo.bar" and "6var". These variables are global. To see a list of currently defined variables use this command:
:let
You can use global variables everywhere. This also means that when the variable "count" is used in one script file, it might also be used in another file. This leads to confusion at least, and real problems at worst. To avoid this, you can use a variable local to a script file by prepending "s:". For example, one script contains this code:
:let s:count = 1
:while s:count < 5
:  source other.vim
:  let s:count += 1
:endwhile
Since "s:count" is local to this script, you can be sure that sourcing the "other.vim" script will not change this variable. If "other.vim" also uses an "s:count" variable, it will be a different copy, local to that script. 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 variable use the ":unlet" command. Example:
:unlet s:count
This deletes the script-local variable "s:count" 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! s:count
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:
:if !exists("s:call_count") : let s:call_count = 0 :endif :let s:call_count = s:call_count + 1 :echo "called" s:call_count "times"
The "exists()" function checks if a variable has already been defined. Its argument is the name of the variable you want to check. Not the variable itself! If you would do this:
:if !exists(s:call_count)
Then the value of s:call_count will be used as the name of the variable that exists() checks. That's not what you want. The exclamation mark ! negates a value. When the value was true, it becomes false. When it was false, it becomes true. You can read it as "not". Thus "if !exists()" can be read as "if not exists()". What Vim calls true is anything that is not zero. Zero is false. Note: Vim automatically converts a string to a number when it is looking for a number. When using a string that doesn't start with a digit the resulting number is zero. Thus look out for this:
:if "true"
The "true" will be interpreted as a zero, thus as false!

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. The type is dynamic, it is set each time when assigning a value to the variable with ":let". More about types in 41.8. To assign a string value to a variable, you need to use a string constant. There are two types of these. First the string in double quotes:
:let name = "peter"
:echo name
peter
If you want to include a double quote inside the string, put a backslash in front of it:
:let name = "\"peter\""
:echo name
"peter"
To avoid the need for a backslash, you can use a string in single quotes:
:let name = '"peter"'
:echo name
"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. 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 rich, yet simple 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 @r register
Examples:
:echo "The value of 'tabstop' is" &ts
:echo "Your home directory is" $HOME
:if @a > 5
The &name form can be used to save an option value, set it to a new value, do something and restore the old value. Example:
:let save_ic = &ic
:set noic
:/The Start/,$delete
:let &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
Strings can be concatenated with ".." (see expr6). Example:
:echo "foo" .. "bar"
foobar
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.
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:
:let i = 4
:echo i > 5 ? "i is big" : "i is small"
i is small
The three parts of the constructs are always evaluated first, thus you could see it work as:
(a) ? (b) : (c)

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 (non-zero) will the {statements} be executed. These must still be valid commands. If they contain garbage, Vim won't be able to find the ":endif". You can also use ":else". The generic form for this is:
:if {condition} {statements} :else {statements} :endif
The second {statements} 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

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 one if the condition is met and zero otherwise. An example:
:if v:version >= 700
:  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. 600 is for version 6.0. Version 6.1 has the value 601. This is very useful to write a script that works with multiple versions of Vim. v:version
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. When comparing a string with a number, the string is first converted to a number. This is a bit tricky, because when a string doesn't look like a number, the number zero is used. Example:
:if 0 == "one"
:  echo "yes"
:endif
This will echo "yes", because "one" doesn't look like a number, thus it is converted to the number zero.
For strings there are two more items:
a =~ b matches with a !~ b does not match with
The left item "a" is used as a string. The right item "b" 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 backslashes would need to be doubled in a double-quote string and patterns tend to contain many backslashes.
The 'ignorecase' option is used when comparing strings. When you don't want that, append "#" to match case and "?" to ignore case. Thus "==?" compares two strings to be equal while ignoring case. And "!~#" checks if a pattern doesn't match, also checking the case of letters. 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:
:while counter < 40
:  call do_something()
:  if skip_flag
:    continue
:  endif
:  if finished_flag
:    break
:  endif
:  sleep 50m
:endwhile
The ":sleep" command makes Vim take a nap. The "50m" specifies fifty milliseconds. Another example is ":sleep 4", which sleeps for four seconds.
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 colon 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 and formats all lines with the "=" operator. To make ":normal" work with an expression, combine ":execute" with it. Example:
:execute "normal " .. normal_commands
The variable "normal_commands" must contain the Normal mode commands. Make sure that the argument for ":normal" is a complete command. Otherwise Vim will run into the end of the argument and abort the command. For example, if you start Insert mode, you must leave Insert mode as well. This works:
:execute "normal Inew text \<Esc>"
This inserts "new text " in the current line. Notice the use of the special key "\<Esc>". This avoids having to enter a real <Esc> character in your script.
If you don't want to execute a string but evaluate it to get its expression value, you can use the eval() function:
:let optname = "path"
:let optval = 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. The same thing can be done with:
:exe 'let optval = &' .. optname

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 ":call" command. The parameters are passed in between parentheses separated by commas. Example:
:call 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.
A function can be called in an expression. Example:
:let line = getline(".")
:let repl = substitute(line, '\a', "*", "g")
:call 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 is the string on which to perform the substitution. The second argument is the pattern, the third the replacement string. Finally, the last arguments are 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-details. 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 matchbufline() all the matches of a pattern in a buffer 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 matchstrlist() all the matches of a pattern in a List of strings 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 strutf16len() number of UTF-16 code units 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 reverse() reverse the order of characters in a string 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 utf16idx() UTF-16 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 foreach() apply function to List items reduce() reduce a List to a value slice() take a slice of a List sort() sort a List reverse() reverse the order of items in a List 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 foreach() apply function to Dictionary 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 reverse() reverse the order of numbers in a blob
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 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 getregion() get a region of text from the buffer getregionpos() get a list of positions for a region 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 writefile() write a List of lines or Blob into a file filecopy() copy a file {from} to {to}
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
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 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 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 (syntax) 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 getcharmod() get modifiers for the last typed character getmousepos() get last known mouse position 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 digraphs digraph_set() register digraph digraph_setlist() register multiple digraphs 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
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
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
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 wait() wait for a condition
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
Context Stack: ctx-functions ctxget() return context at given index from top ctxpop() pop and restore top context ctxpush() push given context ctxset() set context at given index from top ctxsize() return context stack size
Various: various-functions mode() get current editing mode visualmode() last visual mode used exists() check if a variable, function, etc. exists has() check if a feature is supported in Vim changenr() return number of most recent change 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
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 for a buffer
shiftwidth() effective value of 'shiftwidth'
wordcount() get byte/word/char count of buffer
luaeval() evaluate Lua expression py3eval() evaluate Python expression pyeval() evaluate Python expression 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:
:function {name}({var1}, {var2}, ...)
:  {body}
:endfunction
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:
:function Min(num1, num2)
This tells Vim that the function is named "Min" and it takes two arguments: "num1" and "num2". The first thing you need to do is to check to see which number is smaller: 
:  if a:num1 < a:num2
The special prefix "a:" tells Vim that the variable is a function argument. Let's assign the variable "smaller" the value of the smallest number:
:  if a:num1 < a:num2
:    let smaller = a:num1
:  else
:    let smaller = a:num2
:  endif
The variable "smaller" is a local variable. Variables used inside a function are local unless prefixed by something like "g:", "a:", or "s:".
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.
You now use the ":return" statement to return the smallest number to the user. Finally, you end the function:
:  return smaller
:endfunction
The complete function definition is as follows:
:function Min(num1, num2)
:  if a:num1 < a:num2
:    let smaller = a:num1
:  else
:    let smaller = a:num2
:  endif
:  return smaller
:endfunction
For people who like short functions, this does the same thing:
:function Min(num1, num2)
:  if a:num1 < a:num2
:    return a:num1
:  endif
:  return a:num2
:endfunction
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 interpreted 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.
When a function reaches ":endfunction" or ":return" is used without an argument, the function returns zero.
To redefine a function that already exists, use the ! for the ":function" command:
:function!  Min(num1, num2, num3)
USING A RANGE
The ":call" command can be given a line range. This can have one of two meanings. When a function has been defined with the "range" keyword, it will take care of the line range itself. The function will be passed the variables "a:firstline" and "a:lastline". These will have the line numbers from the range the function was called with. Example:
:function Count_words() range
:  let lnum = a:firstline
:  let n = 0
:  while lnum <= a:lastline
:    let n = n + len(split(getline(lnum)))
:    let lnum = lnum + 1
:  endwhile
:  echo "found " .. n .. " words"
:endfunction
You can call this function with:
:10,30call Count_words()
It will be executed once and echo the number of words. The other way to use a line range is by defining a function without the "range" keyword. The function will be called once for every line in the range, with the cursor in that line. Example:
:function  Number()
:  echo "line " .. line(".") .. " contains: " .. getline(".")
:endfunction
If you call this function with:
:10,15call Number()
The function will be called six times.

VARIABLE NUMBER OF ARGUMENTS

Vim enables you to define functions that have a variable number of arguments. The following command, for instance, defines a function that must have 1 argument (start) and can have up to 20 additional arguments:
:function Show(start, ...)
The variable "a:1" contains the first optional argument, "a:2" the second, and so on. The variable "a:0" contains the number of extra arguments. For example:
:function Show(start, ...)
:  echohl Title
:  echo "start is " .. a:start
:  echohl None
:  let index = 1
:  while index <= a:0
:    echo "  Arg " .. index .. " is " .. a:{index}
:    let index = index + 1
:  endwhile
:  echo ""
:endfunction
This uses the ":echohl" command to specify the highlighting used for the following ":echo" command. ":echohl None" stops it again. The ":echon" command works like ":echo", but doesn't output a line break.
You can also use the a:000 variable, it is a List of all the "..." arguments. See a:000.

LISTING FUNCTIONS

The ":function" command lists the names and arguments of all user-defined functions:
:function
function Show(start, ...)
function GetVimIndent()
function SetSyn(name)
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

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 Show() function:
:delfunction Show
You get an error when the function doesn't exist.

FUNCTION REFERENCES

Sometimes it can be useful to have a variable point to one function or another. You can do it with the function() function. It turns the name of a function into a reference:
:let result = 0                " or 1
:function! Right()
:  return 'Right!'
:endfunc
:function! Wrong()
:  return 'Wrong!'
:endfunc
:
:if result == 1
:  let Afunc = function('Right')
:else
:  let Afunc = function('Wrong')
:endif
:echo call(Afunc, [])
Wrong!
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. The way to invoke a function that a variable refers to is with the call() function. Its first argument is the function reference, the second argument is a List with arguments.
Function references are most useful in combination with a Dictionary, as is explained in the next section.
More information about defining your own functions here: user-function.

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 things. The things 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:
:let alist = ['aap', 'mies', 'noot']
The List items are enclosed in square brackets and separated by commas. To create an empty List:
:let alist = []
You can add items to a List with the add() function:
:let alist = []
:call add(alist, 'foo')
:call add(alist, 'bar')
:echo alist
[foo,bar]
List concatenation is done with +:
:echo alist + ['foo', 'bar']
[foo,bar,foo,bar]
Or, if you want to extend a List directly:
:let alist = ['one']
:call extend(alist, ['two', 'three'])
:echo alist
[one,two,three]
Notice that using add() will have a different effect:
:let alist = ['one']
:call add(alist, ['two', 'three'])
:echo alist
[one, [two,three]]
The second argument of add() is added as a single item.

FOR LOOP

One of the nice things you can do with a List is iterate over it:
:let alist = ['one', 'two', 'three']
:for n in alist
:  echo n
:endfor
one
two
three
This will loop over each element in List "alist", assigning the value to variable "n". The generic form of a for loop is:
:for {varname} in {listexpression}
:  {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. 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 lines in the buffer:
:for line in getline(1, 20)
:  if line =~ "Date: "
:    echo matchstr(line, 'Date: \zs.*')
:  endif
:endfor
This looks into lines 1 to 20 (inclusive) and echoes any date found in there.

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:
:let uk2nl = {'one': 'een', 'two': 'twee', 'three': 'drie'}
Now you can lookup words by putting the key in square brackets:
: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.

DICTIONARY FUNCTIONS

The items in a Dictionary can normally be obtained with an index in square brackets:
:echo uk2nl['one']
een
A method that does the same, but without so many punctuation characters:
:echo uk2nl.one
een
This only works for a key that is made of ASCII letters, digits and the underscore. You can also assign a new value this way:
:let uk2nl.four = 'vier'
:echo uk2nl
{'three':drie,four:vier,one:een,two:twee}
And now for something special: you can directly define a function and store a reference to it in the dictionary:
:function uk2nl.translate(line) dict
:  return join(map(split(a:line), 'get(self, v:val, "???")'))
:endfunction
Let's first try it out:
:echo uk2nl.translate('three two five one')
drie twee ??? een
The first special thing you notice is the "dict" at the end of the ":function" line. This marks the function as being used from a Dictionary. The "self" local variable will then refer to that Dictionary. Now let's break up the complicated return command:
split(a:line)
The split() function takes a string, chops it into whitespace separated words and returns a list with these words. Thus in the example it returns:
:echo split('three two five one')
[three,two,five,one]
This list is the first argument to the map() function. This will go through the list, evaluating its second argument with "v:val" set to the value of each item. This is a shortcut to using a for loop. This command:
:let alist = map(split(a:line), 'get(self, v:val, "???")')
Is equivalent to:
:let alist = split(a:line)
:for idx in range(len(alist))
:  let alist[idx] = get(self, alist[idx], "???")
:endfor
The get() function checks if a key is present in a Dictionary. If it is, then the value is retrieved. If it isn't, then the default value is returned, in the example it's '???'. This is a convenient way to handle situations where a key may not be present and you don't want an error message.
The join() function does the opposite of split(): it joins together a list of words, putting a space in between. This combination of split(), map() and join() is a nice way to filter a line of words in a very compact way.

OBJECT ORIENTED PROGRAMMING

Now that you can put both values and functions in a Dictionary, you can actually use a Dictionary like an object. Above we used a Dictionary for translating Dutch to English. We might want to do the same for other languages. Let's first make an object (aka Dictionary) that has the translate function, but no words to translate:
:let transdict = {}
:function transdict.translate(line) dict
:  return join(map(split(a:line), 'get(self.words, v:val, "???")'))
:endfunction
It's slightly different from the function above, using 'self.words' to lookup word translations. But we don't have a self.words. Thus you could call this an abstract class.
Now we can instantiate a Dutch translation object:
:let uk2nl = copy(transdict)
:let uk2nl.words = {'one': 'een', 'two': 'twee', 'three': 'drie'}
:echo uk2nl.translate('three one')
drie een
And a German translator:
:let uk2de = copy(transdict)
:let uk2de.words = {'one': 'eins', 'two': 'zwei', 'three': 'drei'}
:echo uk2de.translate('three one')
drei eins
You see that the copy() function is used to make a copy of the "transdict" Dictionary and then the copy is changed to add the words. The original remains the same, of course.
Now you can go one step further, and use your preferred translator:
:if $LANG =~ "de"
:  let trans = uk2de
:else
:  let trans = uk2nl
:endif
:echo trans.translate('one two three')
een twee drie
Here "trans" refers to one of the two objects (Dictionaries). No copy is made. More about List and Dictionary identity can be found at list-identity and dict-identity.
Now you might use a language that isn't supported. You can overrule the translate() function to do nothing:
:let uk2uk = copy(transdict)
:function! uk2uk.translate(line)
:  return a:line
:endfunction
:echo uk2uk.translate('three one wladiwostok')
three one wladiwostok
Notice that a ! was used to overwrite the existing function reference. Now use "uk2uk" when no recognized language is found:
:if $LANG =~ "de"
:  let trans = uk2de
:elseif $LANG =~ "nl"
:  let trans = uk2nl
:else
:  let trans = uk2uk
:endif
:echo trans.translate('one two three')
one two three
For further reading see Lists and Dictionaries.

41.9 Exceptions

Let's start with an example:
:try
:   read ~/templates/pascal.tmpl
:catch /E484:/
:   echo "Sorry, the Pascal template file cannot be found."
:endtry
The ":read" command will fail if the file does not exist. Instead of generating an error message, this code catches the error and gives the user a nice message.
For the commands in between ":try" and ":endtry" errors are turned into exceptions. An exception is a string. In the case of an error the string contains the error message. And every error message has a number. In this case, the error we catch contains "E484:". This number is guaranteed to stay the same (the text may change, e.g., it may be translated).
When the ":read" command causes another error, the pattern "E484:" will not match in it. Thus this exception will not be caught and result in the usual error message and execution is aborted.
You might be tempted to do this:
:try
:   read ~/templates/pascal.tmpl
:catch
:   echo "Sorry, the Pascal template file cannot be found."
:endtry
This means all errors are caught. But then you will not see errors that are useful, such as "E21: Cannot make changes, 'modifiable' is off".
Another useful mechanism is the ":finally" command:
:let tmp = tempname()
:try
:   exe ".,$write " .. tmp
:   exe "!filter " .. tmp
:   .,$delete
:   exe "$read " .. tmp
:finally
:   call delete(tmp)
:endtry
This filters the lines from the cursor until the end of the file through the "filter" command, which takes a file name argument. No matter if the filtering works, something goes wrong in between ":try" and ":finally" or the user cancels the filtering by pressing CTRL-C, the "call delete(tmp)" is always executed. This makes sure you don't leave the temporary file behind.
More information about exception handling can be found in the reference manual: exception-handling.

41.10 Various remarks

Here is a summary of items that apply to Vim scripts. They are also mentioned elsewhere, but form a nice checklist.
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.

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
The same example written as:
:set tags=my nice file
will issue an error, because it is interpreted as:
:set tags=my
:set nice
:set file

COMMENTS

The character " (the double quote mark) starts a comment. Everything after and including this character 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.
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 todevelopment " 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, causing an error for an unmatched '"' character. 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 cmd                        |" do it
With the '|' character the command is separated from the next one. And that next command is only a comment. For the last command you need to do two things: :execute and use '|':
:exe '!ls *.c'                        |" list C files
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
To spot these problems, you can set the 'list' option when editing vimrc files.
For Unix there is one special way to comment a line, that allows making a Vim script executable:
#!/usr/bin/env vim -S
echo "this is a Vim script"
quit
The "#" command by itself lists a line with the line number. Adding an exclamation mark changes it into doing nothing, so that you can add the shell command to execute the rest of the file. :#! -S

PITFALLS

Even bigger problem arises in the following example:
:map ,ab o#include
:unmap ,ab
Here the unmap command will not work, because it tries to unmap ",ab ". This does not exist as a mapped sequence. An error will be issued, which is very hard to identify, because the ending whitespace character in ":unmap ,ab " is not visible.
And this is the same as what happens when one uses a comment after an "unmap" command:
:unmap ,ab     " comment
Here the comment part will be ignored. However, Vim will try to unmap ',ab ', which does not exist. Rewrite it as:
:unmap ,ab|    " comment

RESTORING THE VIEW

Sometimes you want to make a change and go back to where the cursor was. Restoring the relative position would also be nice, so that the same line appears at the top of the window. This example yanks the current line, puts it above the first line in the file and then restores the view:
map ,p ma"aYHmbgg"aP`bzt`a
What this does:
ma"aYHmbgg"aP`bzt`a
ma set mark a at cursor position "aY yank current line into register a Hmb go to top line in window and set mark b there gg go to first line in file "aP put the yanked line above it b go back to top line in display zt position the text in the window as before a go back to saved cursor position

PACKAGING

To avoid your function names to interfere with functions that you get from others, use this scheme:
Prepend a unique string before each function name. I often use an abbreviation. For example, "OW_" is used for the option window functions.
Put the definition of your functions together in a file. Set a global variable to indicate that the functions have been loaded. When sourcing the file again, first unload the functions. Example:
" This is the XXX package
if exists("XXX_loaded")
  delfun XXX_one
  delfun XXX_two
endif
function XXX_one(a)
        ... body of function ...
endfun
function XXX_two(b)
        ... body of function ...
endfun
let XXX_loaded = 1
============================================================================== 41.11 Writing a plugin write-plugin
You can write a Vim script in such a way that many people can use it. This is called a plugin. Vim users can drop your script in their plugin directory and use its features right away add-plugin.
There are actually two types of plugins:
global plugins: For all types of files. filetype plugins: Only for files of a specific type.
In this section the first type is explained. Most items are also relevant for writing filetype plugins. The specifics for filetype plugins are in the next section write-filetype-plugin.

NAME

First of all you must choose a name for your plugin. The features provided by the plugin should be clear from its name. And it should be unlikely that someone else writes a plugin with the same name but which does something different. And please limit the name to 8 characters, to avoid problems on old MS-Windows systems.
A script that corrects typing mistakes could be called "typecorr.vim". We will use it here as an example.
For the plugin to work for everybody, it should follow a few guidelines. This will be explained step-by-step. The complete example plugin is at the end.

BODY

Let's start with the body of the plugin, the lines that do the actual work:
14        iabbrev teh the
15        iabbrev otehr other
16        iabbrev wnat want
17        iabbrev synchronisation
18                \ synchronization
19        let s:count = 4
The actual list should be much longer, of course.
The line numbers have only been added to explain a few things, don't put them in your plugin file!

HEADER

You will probably add new corrections to the plugin and soon have several versions lying around. And when distributing this file, people will want to know who wrote this wonderful plugin and where they can send remarks. Therefore, put a header at the top of your plugin:
1        " Vim global plugin for correcting typing mistakes
2        " Last Change:        2000 Oct 15
3        " Maintainer:        Bram Moolenaar <[email protected]>
About copyright and licensing: Since plugins are very useful and it's hardly worth restricting their distribution, please consider making your plugin either public domain or use the Vim license. A short note about this near the top of the plugin should be sufficient. Example:
4        " License:        This file is placed in the public domain.
LINE CONTINUATION, AVOIDING SIDE EFFECTS use-cpo-save
In line 18 above, the line-continuation mechanism is used line-continuation. Users with 'compatible' set will run into trouble here, they will get an error message. We can't just reset 'compatible', because that has a lot of side effects. To avoid this, we will set the 'cpoptions' option to its Vim default value and restore it later. That will allow the use of line-continuation and make the script work for most people. It is done like this:
11        let s:save_cpo = &cpo
12        set cpo&vim
..
42        let &cpo = s:save_cpo
43        unlet s:save_cpo
We first store the old value of 'cpoptions' in the s:save_cpo variable. At the end of the plugin this value is restored.
Notice that a script-local variable is used s:var. A global variable could already be in use for something else. Always use script-local variables for things that are only used in the script.

NOT LOADING

It's possible that a user doesn't always want to load this plugin. Or the system administrator has dropped it in the system-wide plugin directory, but a user has their own plugin they want to use. Then the user must have a chance to disable loading this specific plugin. This will make it possible:
6        if exists("g:loaded_typecorr")
7          finish
8        endif
9        let g:loaded_typecorr = 1
This also avoids that when the script is loaded twice it would cause error messages for redefining functions and cause trouble for autocommands that are added twice.
The name is recommended to start with "loaded_" and then the file name of the plugin, literally. The "g:" is prepended just to avoid mistakes when using the variable in a function (without "g:" it would be a variable local to the function).
Using "finish" stops Vim from reading the rest of the file, it's much quicker than using if-endif around the whole file.

MAPPING

Now let's make the plugin more interesting: We will add a mapping that adds a correction for the word under the cursor. We could just pick a key sequence for this mapping, but the user might already use it for something else. To allow the user to define which keys a mapping in a plugin uses, the <Leader> item can be used:
22          map <unique> <Leader>a  <Plug>TypecorrAdd;
The "<Plug>TypecorrAdd;" thing will do the work, more about that further on.
The user can set the "mapleader" variable to the key sequence that they want this mapping to start with. Thus if the user has done:
let mapleader = "_"
the mapping will define "_a". If the user didn't do this, the default value will be used, which is a backslash. Then a map for "\a" will be defined.
Note that <unique> is used, this will cause an error message if the mapping already happened to exist. :map-<unique>
But what if the user wants to define their own key sequence? We can allow that with this mechanism:
21        if !hasmapto('<Plug>TypecorrAdd;')
22          map <unique> <Leader>a  <Plug>TypecorrAdd;
23        endif
This checks if a mapping to "<Plug>TypecorrAdd;" already exists, and only defines the mapping from "<Leader>a" if it doesn't. The user then has a chance of putting this in their vimrc file:
map ,c  <Plug>TypecorrAdd;
Then the mapped key sequence will be ",c" instead of "_a" or "\a".

PIECES

If a script gets longer, you often want to break up the work in pieces. You can use functions or mappings for this. But you don't want these functions and mappings to interfere with the ones from other scripts. For example, you could define a function Add(), but another script could try to define the same function. To avoid this, we define the function local to the script by prepending it with "s:".
We will define a function that adds a new typing correction:
30        function s:Add(from, correct)
31          let to = input("type the correction for " .. a:from .. ": ")
32          exe ":iabbrev " .. a:from .. " " .. to
..
36        endfunction
Now we can call the function s:Add() from within this script. If another script also defines s:Add(), it will be local to that script and can only be called from the script it was defined in. There can also be a global Add() function (without the "s:"), which is again another function.
<SID> can be used with mappings. It generates a script ID, which identifies the current script. In our typing correction plugin we use it like this:
24        noremap <unique> <script> <Plug>TypecorrAdd;  <SID>Add
..
28        noremap <SID>Add  :call <SID>Add(expand("<cword>"), 1)<CR>
Thus when a user types "\a", this sequence is invoked:
\a  ->  <Plug>TypecorrAdd;  ->  <SID>Add  ->  :call <SID>Add()
If another script also maps <SID>Add, it will get another script ID and thus define another mapping.
Note that instead of s:Add() we use <SID>Add() here. That is because the mapping is typed by the user, thus outside of the script. The <SID> is translated to the script ID, so that Vim knows in which script to look for the Add() function.
This is a bit complicated, but it's required for the plugin to work together with other plugins. The basic rule is that you use <SID>Add() in mappings and s:Add() in other places (the script itself, autocommands, user commands).
We can also add a menu entry to do the same as the mapping:
26        noremenu <script> Plugin.Add\ Correction      <SID>Add
The "Plugin" menu is recommended for adding menu items for plugins. In this case only one item is used. When adding more items, creating a submenu is recommended. For example, "Plugin.CVS" could be used for a plugin that offers CVS operations "Plugin.CVS.checkin", "Plugin.CVS.checkout", etc.
Note that in line 28 ":noremap" is used to avoid that any other mappings cause trouble. Someone may have remapped ":call", for example. In line 24 we also use ":noremap", but we do want "<SID>Add" to be remapped. This is why "<script>" is used here. This only allows mappings which are local to the script. :map-<script> The same is done in line 26 for ":noremenu". :menu-<script>
<SID> AND <Plug> using-<Plug>
Both <SID> and <Plug> are used to avoid that mappings of typed keys interfere with mappings that are only to be used from other mappings. Note the difference between using <SID> and <Plug>:
<Plug> is visible outside of the script. It is used for mappings which the user might want to map a key sequence to. <Plug> is a special code that a typed key will never produce. To make it very unlikely that other plugins use the same sequence of characters, use this structure: <Plug> scriptname mapname In our example the scriptname is "Typecorr" and the mapname is "Add". We add a semicolon as the terminator. This results in "<Plug>TypecorrAdd;". Only the first character of scriptname and mapname is uppercase, so that we can see where mapname starts.
<SID> is the script ID, a unique identifier for a script. Internally Vim translates <SID> to "<SNR>123_", where "123" can be any number. Thus a function "<SID>Add()" will have a name "<SNR>11_Add()" in one script, and "<SNR>22_Add()" in another. You can see this if you use the ":function" command to get a list of functions. The translation of <SID> in mappings is exactly the same, that's how you can call a script-local function from a mapping.

USER COMMAND

Now let's add a user command to add a correction:
38        if !exists(":Correct")
39          command -nargs=1  Correct  :call s:Add(<q-args>, 0)
40        endif
The user command is defined only if no command with the same name already exists. Otherwise we would get an error here. Overriding the existing user command with ":command!" is not a good idea, this would probably make the user wonder why the command they defined themself doesn't work. :command

SCRIPT VARIABLES

When a variable starts with "s:" it is a script variable. It can only be used inside a script. Outside the script it's not visible. This avoids trouble with using the same variable name in different scripts. The variables will be kept as long as Vim is running. And the same variables are used when sourcing the same script again. s:var
The fun is that these variables can also be used in functions, autocommands and user commands that are defined in the script. In our example we can add a few lines to count the number of corrections:
19        let s:count = 4
..
30        function s:Add(from, correct)
..
34          let s:count = s:count + 1
35          echo s:count .. " corrections now"
36        endfunction
First s:count is initialized to 4 in the script itself. When later the s:Add() function is called, it increments s:count. It doesn't matter from where the function was called, since it has been defined in the script, it will use the local variables from this script.

THE RESULT

Here is the resulting complete example:
 1        " Vim global plugin for correcting typing mistakes
 2        " Last Change:        2000 Oct 15
 3        " Maintainer:        Bram Moolenaar <[email protected]>
 4        " License:        This file is placed in the public domain.
 5
 6        if exists("g:loaded_typecorr")
 7          finish
 8        endif
 9        let g:loaded_typecorr = 1
10
11        let s:save_cpo = &cpo
12        set cpo&vim
13
14        iabbrev teh the
15        iabbrev otehr other
16        iabbrev wnat want
17        iabbrev synchronisation
18                \ synchronization
19        let s:count = 4
20
21        if !hasmapto('<Plug>TypecorrAdd;')
22          map <unique> <Leader>a  <Plug>TypecorrAdd;
23        endif
24        noremap <unique> <script> <Plug>TypecorrAdd;  <SID>Add
25
26        noremenu <script> Plugin.Add\ Correction      <SID>Add
27
28        noremap <SID>Add  :call <SID>Add(expand("<cword>"), 1)<CR>
29
30        function s:Add(from, correct)
31          let to = input("type the correction for " .. a:from .. ": ")
32          exe ":iabbrev " .. a:from .. " " .. to
33          if a:correct | exe "normal viws\<C-R>\" \b\e" | endif
34          let s:count = s:count + 1
35          echo s:count .. " corrections now"
36        endfunction
37
38        if !exists(":Correct")
39          command -nargs=1  Correct  :call s:Add(<q-args>, 0)
40        endif
41
42        let &cpo = s:save_cpo
43        unlet s:save_cpo
Line 33 wasn't explained yet. It applies the new correction to the word under the cursor. The :normal command is used to use the new abbreviation. Note that mappings and abbreviations are expanded here, even though the function was called from a mapping defined with ":noremap".
Using "unix" for the 'fileformat' option is recommended. The Vim scripts will then work everywhere. Scripts with 'fileformat' set to "dos" do not work on Unix. Also see :source_crnl. To be sure it is set right, do this before writing the file:
:set fileformat=unix

DOCUMENTATION write-local-help

It's a good idea to also write some documentation for your plugin. Especially when its behavior can be changed by the user. See add-local-help for how they are installed.
Here is a simple example for a plugin help file, called "typecorr.txt":
 1        *typecorr.txt*        Plugin for correcting typing mistakes
 2
 3        If you make typing mistakes, this plugin will have them corrected
 4        automatically.
 5
 6        There are currently only a few corrections.  Add your own if you like.
 7
 8        Mappings:
 9        <Leader>a   or   <Plug>TypecorrAdd;
10                Add a correction for the word under the cursor.
11
12        Commands:
13        :Correct {word}
14                Add a correction for {word}.
15
16                                                        *typecorr-settings*
17        This plugin doesn't have any settings.
The first line is actually the only one for which the format matters. It will be extracted from the help file to be put in the "LOCAL ADDITIONS:" section of first line. After adding your help file do ":help" and check that the entries line up nicely.
You can add more tags inside ** in your help file. But be careful not to use existing help tags. You would probably use the name of your plugin in most of them, like "typecorr-settings" in the example.
Using references to other parts of the help in || is recommended. This makes it easy for the user to find associated help.

FILETYPE DETECTION plugin-filetype

If your filetype is not already detected by Vim, you should create a filetype detection snippet in a separate file. It is usually in the form of an autocommand that sets the filetype when the file name matches a pattern. Example:
au BufNewFile,BufRead *.foo                        set filetype=foofoo
Write this single-line file as "ftdetect/foofoo.vim" in the first directory that appears in 'runtimepath'. For Unix that would be "~/.config/nvim/ftdetect/foofoo.vim". The convention is to use the name of the filetype for the script name.
You can make more complicated checks if you like, for example to inspect the contents of the file to recognize the language. Also see new-filetype.

SUMMARY plugin-special

Summary of special things to use in a plugin:
s:name Variables local to the script.
<SID> Script-ID, used for mappings and functions local to the script.
hasmapto() Function to test if the user already defined a mapping for functionality the script offers.
<Leader> Value of "mapleader", which the user defines as the keys that plugin mappings start with.
:map <unique> Give a warning if a mapping already exists.
:noremap <script> Use only mappings local to the script, not global mappings.
exists(":Cmd") Check if a user command already exists.

41.12 Writing a filetype plugin write-filetype-plugin ftplugin

A filetype plugin is like a global plugin, except that it sets options and defines mappings for the current buffer only. See add-filetype-plugin for how this type of plugin is used.
First read the section on global plugins above 41.11. All that is said there also applies to filetype plugins. There are a few extras, which are explained here. The essential thing is that a filetype plugin should only have an effect on the current buffer.

DISABLING

If you are writing a filetype plugin to be used by many people, they need a chance to disable loading it. Put this at the top of the plugin:
" Only do this when not done yet for this buffer
if exists("b:did_ftplugin")
  finish
endif
let b:did_ftplugin = 1
This also needs to be used to avoid that the same plugin is executed twice for the same buffer (happens when using an ":edit" command without arguments).
Now users can disable loading the default plugin completely by making a filetype plugin with only this line:
let b:did_ftplugin = 1
This does require that the filetype plugin directory comes before $VIMRUNTIME in 'runtimepath'!
If you do want to use the default plugin, but overrule one of the settings, you can write the different setting in a script:
setlocal textwidth=70
Now write this in the "after" directory, so that it gets sourced after the distributed "vim.vim" ftplugin after-directory. For Unix this would be "~/.config/nvim/after/ftplugin/vim.vim". Note that the default plugin will have set "b:did_ftplugin", but it is ignored here.

OPTIONS

To make sure the filetype plugin only affects the current buffer use the
:setlocal
command to set options. And only set options which are local to a buffer (see the help for the option to check that). When using :setlocal for global options or options local to a window, the value will change for many buffers, and that is not what a filetype plugin should do.
When an option has a value that is a list of flags or items, consider using "+=" and "-=" to keep the existing value. Be aware that the user may have changed an option value already. First resetting to the default value and then changing it is often a good idea. Example:
:setlocal formatoptions& formatoptions+=ro

MAPPINGS

To make sure mappings will only work in the current buffer use the
:map <buffer>
command. This needs to be combined with the two-step mapping explained above. An example of how to define functionality in a filetype plugin:
if !hasmapto('<Plug>JavaImport;')
  map <buffer> <unique> <LocalLeader>i <Plug>JavaImport;
endif
noremap <buffer> <unique> <Plug>JavaImport; oimport ""<Left><Esc>
hasmapto() is used to check if the user has already defined a map to <Plug>JavaImport;. If not, then the filetype plugin defines the default mapping. This starts with <LocalLeader>, which allows the user to select the key(s) they want filetype plugin mappings to start with. The default is a backslash. "<unique>" is used to give an error message if the mapping already exists or overlaps with an existing mapping. :noremap is used to avoid that any other mappings that the user has defined interferes. You might want to use ":noremap <script>" to allow remapping mappings defined in this script that start with <SID>.
The user must have a chance to disable the mappings in a filetype plugin, without disabling everything. Here is an example of how this is done for a plugin for the mail filetype:
" Add mappings, unless the user didn't want this.
if !exists("no_plugin_maps") && !exists("no_mail_maps")
  " Quote text by inserting "> "
  if !hasmapto('<Plug>MailQuote;')
    vmap <buffer> <LocalLeader>q <Plug>MailQuote;
    nmap <buffer> <LocalLeader>q <Plug>MailQuote;
  endif
  vnoremap <buffer> <Plug>MailQuote; :s/^/> /<CR>
  nnoremap <buffer> <Plug>MailQuote; :.,$s/^/> /<CR>
endif
Two global variables are used: no_plugin_maps disables mappings for all filetype plugins no_mail_maps disables mappings for the "mail" filetype

USER COMMANDS

To add a user command for a specific file type, so that it can only be used in one buffer, use the "-buffer" argument to :command. Example:
:command -buffer  Make  make %:r.s

VARIABLES

A filetype plugin will be sourced for each buffer of the type it's for. Local script variables s:var will be shared between all invocations. Use local buffer variables b:var if you want a variable specifically for one buffer.

FUNCTIONS

When defining a function, this only needs to be done once. But the filetype plugin will be sourced every time a file with this filetype will be opened. This construct makes sure the function is only defined once:
:if !exists("*s:Func")
:  function s:Func(arg)
:    ...
:  endfunction
:endif

UNDO undo_indent undo_ftplugin

When the user does ":setfiletype xyz" the effect of the previous filetype should be undone. Set the b:undo_ftplugin variable to the commands that will undo the settings in your filetype plugin. Example:
let b:undo_ftplugin = "setlocal fo< com< tw< commentstring<"
        \ .. "| unlet b:match_ignorecase b:match_words b:match_skip"
Using ":setlocal" with "<" after the option name resets the option to its global value. That is mostly the best way to reset the option value.
This does require removing the "C" flag from 'cpoptions' to allow line continuation, as mentioned above use-cpo-save.
For undoing the effect of an indent script, the b:undo_indent variable should be set accordingly.

FILE NAME

The filetype must be included in the file name ftplugin-name. Use one of these three forms:
.../ftplugin/stuff.vim .../ftplugin/stuff_foo.vim .../ftplugin/stuff/bar.vim
"stuff" is the filetype, "foo" and "bar" are arbitrary names.

SUMMARY ftplugin-special

Summary of special things to use in a filetype plugin:
<LocalLeader> Value of "maplocalleader", which the user defines as the keys that filetype plugin mappings start with.
:map <buffer> Define a mapping local to the buffer.
:noremap <script> Only remap mappings defined in this script that start with <SID>.
:setlocal Set an option for the current buffer only.
:command -buffer Define a user command local to the buffer.
exists("*s:Func") Check if a function was already defined.
Also see plugin-special, the special things used for all plugins.

41.13 Writing a compiler plugin write-compiler-plugin

A compiler plugin sets options for use with a specific compiler. The user can load it with the :compiler command. The main use is to set the 'errorformat' and 'makeprg' options.
Easiest is to have a look at examples. This command will edit all the default compiler plugins:
:next $VIMRUNTIME/compiler/*.vim
Use :next to go to the next plugin file.
There are two special items about these files. First is a mechanism to allow a user to overrule or add to the default file. The default files start with:
:if exists("current_compiler")
:  finish
:endif
:let current_compiler = "mine"
When you write a compiler file and put it in your personal runtime directory (e.g., ~/.config/nvim/compiler for Unix), you set the "current_compiler" variable to make the default file skip the settings. :CompilerSet The second mechanism is to use ":set" for ":compiler!" and ":setlocal" for ":compiler". Vim defines the ":CompilerSet" user command for this. This is an example:
CompilerSet errorformat&                " use the default 'errorformat'
CompilerSet makeprg=nmake
When you write a compiler plugin for the Vim distribution or for a system-wide runtime directory, use the mechanism mentioned above. When "current_compiler" was already set by a user plugin nothing will be done.
When you write a compiler plugin to overrule settings from a default plugin, don't check "current_compiler". This plugin is supposed to be loaded last, thus it should be in a directory at the end of 'runtimepath'. For Unix that could be ~/.config/nvim/after/compiler.

41.14 Writing a plugin that loads quickly write-plugin-quickload

A plugin may grow and become quite long. The startup delay may become noticeable, while you hardly ever use the plugin. Then it's time for a quickload plugin.
The basic idea is that the plugin is loaded twice. The first time user commands and mappings are defined that offer the functionality. The second time the functions that implement the functionality are defined.
It may sound surprising that quickload means loading a script twice. What we mean is that it loads quickly the first time, postponing the bulk of the script to the second time, which only happens when you actually use it. When you always use the functionality it actually gets slower!
Note that since Vim 7 there is an alternative: use the autoload functionality 41.15.
The following example shows how it's done:
" Vim global plugin for demonstrating quick loading
" Last Change:        2005 Feb 25
" Maintainer:        Bram Moolenaar <[email protected]>
" License:        This file is placed in the public domain.
if !exists("s:did_load")
        command -nargs=* BNRead  call BufNetRead(<f-args>)
        map <F19> :call BufNetWrite('something')<CR>
        let s:did_load = 1
        exe 'au FuncUndefined BufNet* source ' .. expand('<sfile>')
        finish
endif
function BufNetRead(...)
        echo 'BufNetRead(' .. string(a:000) .. ')'
        " read functionality here
endfunction
function BufNetWrite(...)
        echo 'BufNetWrite(' .. string(a:000) .. ')'
        " write functionality here
endfunction
When the script is first loaded "s:did_load" is not set. The commands between the "if" and "endif" will be executed. This ends in a :finish command, thus the rest of the script is not executed.
The second time the script is loaded "s:did_load" exists and the commands after the "endif" are executed. This defines the (possible long) BufNetRead() and BufNetWrite() functions.
If you drop this script in your plugin directory Vim will execute it on startup. This is the sequence of events that happens:
1. The "BNRead" command is defined and the <F19> key is mapped when the script is sourced at startup. A FuncUndefined autocommand is defined. The ":finish" command causes the script to terminate early.
2. The user types the BNRead command or presses the <F19> key. The BufNetRead() or BufNetWrite() function will be called.
3. Vim can't find the function and triggers the FuncUndefined autocommand event. Since the pattern "BufNet*" matches the invoked function, the command "source fname" will be executed. "fname" will be equal to the name of the script, no matter where it is located, because it comes from expanding "<sfile>" (see expand()).
4. The script is sourced again, the "s:did_load" variable exists and the functions are defined.
Notice that the functions that are loaded afterwards match the pattern in the FuncUndefined autocommand. You must make sure that no other plugin defines functions that match this pattern.

41.15 Writing library scripts write-library-script

Some functionality will be required in several places. When this becomes more than a few lines you will want to put it in one script and use it from many scripts. We will call that one script a library script.
Manually loading a library script is possible, so long as you avoid loading it when it's already done. You can do this with the exists() function. Example:
if !exists('*MyLibFunction')
   runtime library/mylibscript.vim
endif
call MyLibFunction(arg)
Here you need to know that MyLibFunction() is defined in a script "library/mylibscript.vim" in one of the directories in 'runtimepath'.
To make this a bit simpler Vim offers the autoload mechanism. Then the example looks like this:
call mylib#myfunction(arg)
That's a lot simpler, isn't it? Vim will recognize the function name and when it's not defined search for the script "autoload/mylib.vim" in 'runtimepath'. That script must define the "mylib#myfunction()" function.
You can put many other functions in the mylib.vim script, you are free to organize your functions in library scripts. But you must use function names where the part before the '#' matches the script name. Otherwise Vim would not know what script to load.
If you get really enthusiastic and write lots of library scripts, you may want to use subdirectories. Example:
call netlib#ftp#read('somefile')
For Unix the library script used for this could be:
~/.config/nvim/autoload/netlib/ftp.vim
Where the function is defined like this:
function netlib#ftp#read(fname)
        "  Read the file fname through ftp
endfunction
Notice that the name the function is defined with is exactly the same as the name used for calling the function. And the part before the last '#' exactly matches the subdirectory and script name.
You can use the same mechanism for variables:
let weekdays = dutch#weekdays
This will load the script "autoload/dutch.vim", which should contain something like:
let dutch#weekdays = ['zondag', 'maandag', 'dinsdag', 'woensdag',
        \ 'donderdag', 'vrijdag', 'zaterdag']
Further reading: autoload.

41.16 Distributing Vim scripts distribute-script

Vim users will look for scripts on the Vim website: https://www.vim.org. If you made something that is useful for others, share it!
Vim scripts can be used on any system. There might not be a tar or gzip command. If you want to pack files together and/or compress them the "zip" utility is recommended.
Next chapter: usr_42.txt Add new menus
Copyright: see manual-copyright vim:tw=78:ts=8:noet:ft=help:norl:
Main
Commands index
Quick reference
Introduction
Variables
Expressions
Conditionals
Executing an expression
Using functions
Defining a function
Lists and Dictionaries
Exceptions
Various remarks
Writing a filetype plugin
Writing a compiler plugin
Writing a plugin that loads quickly
Writing library scripts
Distributing Vim scripts