# Vim documentation: usr_41

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    *usr_41.txt*	For Vim version 6.0ar.  Last change: 2001 Aug 07

    		     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|	Various remarks
    |41.9|	Writing a plugin
    |41.10|	Writing a filetype plugin
    |41.11|	Writing a compiler plugin

         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			*vimrc-intro* *vim-script-intro*

    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.

    Let's start with a simple example:

    	:let i = 1
    	:while i < 5
    	:  echo "count is" i
    	:  let i = 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.

    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.
       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 another ":let i =" command.  The value used is the expression "i
    + 1".  This adds one to the variable i and assigns the new value to the same
    variable.
       The output of the example code is:

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

    	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).

    THREE KINDS OF NUMBERS

    Numbers can be decimal, hexadecimal or octal.  A hexadecimal number starts
    with "0x" or "0X".  For example "0x1f" is 31.  An octal number starts with a
    zero.  "017" is 15.  Careful: don't put a zero before a decimal number, it
    will be intepreted as an octal number!
       The ":echo" command always prints decimal numbers.  Example:

    	:echo 0x7f 036
     	127 30

    A number is made negative with a minus sign.  This also works for hexadecimal
    and octal numbers.   A minus sign is also for substraction.  Compare this with
    the previous example:

    	:echo 0x7f -036
     	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, put a space between the minus sign
    and the following number:

    	:echo 0x7f - 036

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

    *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_dashes
    	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 = 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 finishes, the local variables used there will not be
    automatically freed.  The next time the script executes, it can still use the
    old value.  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.  Only zero is 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 only two types of variables that Vim
    supports.  The type is dynamic, it is set each time when assigning a value to
    the variable with ":let".
       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 taken literally.  The
    drawback is that it's impossible to include a single quote.  A backslash is
    taken literally as well, 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 &option 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.

    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 braces.  No suprises here.  Example:

    	:echo (10 + 5) * 2
     	30

    Strings can be concatenated with ".".  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 >= 600
    	:  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 will have 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"
    	:elseif str !~ '\.$'
    	:  echo "str ends in a full stop"
    	:endif

    Notice the use of a single-quote string for the pattern.  This is useful,
    because backslashes 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.

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

    *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.

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

    *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 here: |functions|.

    A function is called with the ":call" command.  The parameters are passed in
    between braces, 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 file.  Its argument is
    a specification of the line number.  In this case "." is used, which means the
    line where the cursor.
       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 more 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: |functions|.  Use CTRL-] on
    the function name to jump to detailed help on it.

    String manipulation:
    	char2nr()		get ASCII value of a character
    	nr2char()		get a character by its ASCII value
    	escape()		escape characters in a string with a '\'
    	strtrans()		translate a string to make it printable
    	tolower()		turn a string to lowercase
    	toupper()		turn a string to uppercase
    	match()			position where a pattern matches in a string
    	matchend()		position where a pattern match ends in a string
    	matchstr()		match of a pattern in a string
    	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
    	substitute()		substitute a pattern match with a string
    	submatch()		get a specific match in a ":substitute"
    	strpart()		get part of a string
    	expand()		expand special keywords
    	type()			type of a variable

    Working with text in the current buffer:
    	byte2line()		get line number at a specific byte count
    	line2byte()		byte count at a specific line
    	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
    	getline()		get a line from the buffer
    	setline()		replace a line in the buffer
    	append()		append {string} below line {lnum}
    	indent()		indent of a specific line
    	nextnonblank()		find next non-blank line
    	prevnonblank()		find previous non-blank line
    	search()		find a match for a pattern
    	searchpair()		find the other end of a start/skip/end

    System functions and manipulation of files:
    	browse()		put up a file requester
    	glob()			expand wildcards
    	globpath()		expand wildcards in a number of directories
    	resolve()		find out where a shortcut points to
    	fnamemodify()		modify a file name
    	executable()		check if an executable program exists
    	filereadable()		check if a file can be read
    	isdirectory()		check if a directory exists
    	getcwd()		get the current working directory
    	getfsize()		get the size of a file
    	getftime()		get last modification time of a file
    	localtime()		get current time
    	strftime()		convert time to a string
    	tempname()		get the name of a temporary file
    	delete()		delete a file
    	rename()		rename a file
    	system()		get the result of a shell command
    	hostname()		name of the system

    Buffers, windows and the argument list:
    	argc()			number of entries in the argument list
    	argidx()		current position in the argument list
    	argv()			get one entry from the argument list
    	bufexists()		check if a buffer exists
    	buflisted()		check if a buffer exists and is listed
    	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
    	winnr()			get the window number for the current window
    	bufwinnr()		get the window number of a specific buffer
    	winbufnr()		get the buffer number of a specific window
    	getbufvar()		get a variable value from a specific buffer
    	setbufvar()		set a variable in a specific buffer
    	getwinvar()		get a variable value from a specific window
    	setwinvar()		set a variable in a specific buffer

    Folding:
    	foldclosed()		check for a closed fold at a specific line
    	foldlevel()		check for the fold level at a specific line
    	foldtext()		generate the line displayed for a closed fold

    Syntax highlighting:
    	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

    History:
    	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:
    	confirm()		let the user make a choice
    	getchar()		get a character from the user
    	getcharmod()		get modifiers for the last typed character
    	input()			get a line from the user
    	inputsecret()		get a line from the user without showing it
    	inputdialog()		get a line from the user in a dialog

    Various:
    	mode()			get current editing mode
    	visualmode()		last visual mode used
    	hasmapto()		check if a mapping exists
    	mapcheck()		check if a matching mapping exists
    	maparg()		get rhs of a mapping
    	exists()		check if a variable, function, etc. exists
    	has()			check if a feature is supported in Vim
    	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
    	getwinposx()		X position of the GUI Vim window
    	getwinposy()		Y position of the GUI Vim window
    	winheight()		get height of a specific window
    	winwidth()		get width of a specific window
    	libcall()		call a function in an external library
    	libcallnr()		idem, returning a number

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

    *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:count" inside a function is used for the global
    	variable "count", and "count" 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

    A user defined function is called in exactly the same way a a builtin
    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 n = a:firstline
    	:  let count = 0
    	:  while n <= a:lastline
    	:    let count = count + Wordcount(getline(n))
    	:  endwhile
    	:  echo "found " . count . " 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 "Show is " . a:start
    	:  echohl None
    	:  let index = 1
    	:  while index <= a:0
    	:    execute 'echon "  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.

    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 Show
     	1          :  echo "Show is " . a:start
    	2          :  let index = 1
    	3          :  while index <= a:0
    	4          :    execute 'echo "Arg " . index . " is " . a:' . index
    	5          :    let index = index + 1
    	6          :  endwhile
    	   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.

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

    *41.8*	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 Unix a single <NL>
    character is used.  For MS-DOS, Windows, OS/2 and the like, <CR><LF> is used.
    This is important when using mappings that end in a <CR>.  See |:source_crnl|.

    WHITE SPACE

    Blank lines are allowed and ignored.

    Leading whitespace characters (blanks and TABs) are always ignored.  The
    whitespaces between parameters (e.g. between the 'set' and the 'cpoptions' in the
    example below) are reduced to one blank character and plays the role of a
    separator, the whitespaces after the last (visible) character may or may not
    be ignored depending on the situation, see below.

    For a ":set" command involving the "=" (equal) sign, such as in:

    	:set cpoptions    =aABceFst

    The whitespace immediately before the "=" sign is ignored.  But there can be
    no whitespace after the "=" sign!

    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 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, 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.

    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 avoid these problems, you can set the 'list' option when editing vimrc
    files.

    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 on the '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.  Rewreite it as:

    	:unmap ,ab|" comment

    RESTORING THE VIEW

    Sometimes you want to make a change and go back to where 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

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

    *41.9*	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 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:

     13	iabbrev teh the
     14	iabbrev otehr other
     15	iabbrev wnat want
     16	iabbrev synchronisation
     17		\ synchronization
     18	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 laying 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 <Bram@vim.org>

    LINE CONTINUATION, AVOIDING SIDE EFFECTS

    In line 17 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:

     10	let s:save_cpo = &cpo
     11	set cpo&vim
     ..
     41	let &cpo = 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 his own plugin he wants to use.  Then the user must have a chance to
    disable loading this specific plugin.  This will make it possible:

      5	if exists("loaded_typecorr")
      6	  finish
      7	endif
      8	let 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.

    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:

     21	  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 he wants
    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 his own key sequence?  We can allow that
    with this mechanism:

     20	if !hasmapto('<Plug>TypecorrAdd')
     21	  map <unique> <Leader>a  <Plug>TypecorrAdd
     22	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 his 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:

     29	function s:Add(from, correct)
     30	  let to = input("type the correction for " . a:from . ": ")
     31	  exe ":iabbrev " . a:from . " " . to
     ..
     35	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:

     23	noremap <unique> <script> <Plug>TypecorrAdd  <SID>Add
     ..
     27	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 would also map <SID>Add, it would 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:

     25	noremenu <script> Tools.Add\ Correction      <SID>Add

    Note that in line 27 ":noremap" is used to avoid that any other mappings cause
    trouble.  Someone may have remapped ":call", for example.  In line 23 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 25 for ":noremenu".
    |:menu-<script>|

    <SID> AND <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".
    	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:

     37	if !exists(":Correct")
     38	  command -nargs=1  Correct  :call s:Add(<q-args>, 0)
     39	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 he defined himself 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:

     18	let s:count = 4
     ..
     29	function s:Add(from, correct)
     ..
     33	  let s:count = s:count + 1
     34	  echo s:count . " corrections now"
     35	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 <Bram@vim.org>
      4
      5	if exists("loaded_typecorr")
      6	  finish
      7	endif
      8	let loaded_typecorr = 1
      9
     10	let s:save_cpo = &cpo
     11	set cpo&vim
     12
     13	iabbrev teh the
     14	iabbrev otehr other
     15	iabbrev wnat want
     16	iabbrev synchronisation
     17		\ synchronization
     18	let s:count = 4
     19
     20	if !hasmapto('<Plug>TypecorrAdd')
     21	  map <unique> <Leader>a  <Plug>TypecorrAdd
     22	endif
     23	noremap <unique> <script> <Plug>TypecorrAdd  <SID>Add
     24
     25	noremenu <script> Tools.Add\ Correction      <SID>Add
     26
     27	noremap <SID>Add  :call <SID>Add(expand("<cword>"), 1)<CR>
     28
     29	function s:Add(from, correct)
     30	  let to = input("type the correction for " . a:from . ": ")
     31	  exe ":iabbrev " . a:from . " " . to
     32	  if a:correct | exe "normal viws\<C-R>\" \b\e" | endif
     33	  let s:count = s:count + 1
     34	  echo s:count . " corrections now"
     35	endfunction
     36
     37	if !exists(":Correct")
     38	  command -nargs=1  Correct  :call s:Add(<q-args>, 0)
     39	endif
     40
     41	let &cpo = s:save_cpo

    Line 32 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".

    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
    help.txt.  The first "*" must be in the first column of the first line.

    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.

    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.

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

    *41.10*	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 |41.7|.  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 make a filetype plugin like this:

    	source $VIMRUNTIME/ftplugin/vim.vim
    	set textwidth=70

    This first loads the default filetype plugin to get all its settings.  Then
    the value for the 'textwidth' option is changed to "70".  Note that the
    default plugin will have set "b:did_ftplugin", thus when it's sourced later,
    it won't do anything.

    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 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 funcionality 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) he wants 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 a specific 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 make sure the function is only defined once:

    	:if !exists("*s:Func")
    	:  function s:Func(arg)
    	:    ...
    	:  endfunction
    	:endif

    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.

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

    *41.11*	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.

    The only special item about these files 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., ~/.vim/runtime/compiler for Unix), you set the "current_compiler"
    variable to make the default file skip the settings.

    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 ~/.vim/runtime/after/compiler.

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

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