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usr_41.txt    For Vim version 7.4.  Last change: 2014 Aug 16

                     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

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

Your first experience with Vim scripts is the vimrc file.  Vim reads it when
it starts up and executes the commands.  You can set options to 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 += 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.


THREE KINDS OF NUMBERS

Numbers can be decimal, hexadecimal or octal.  A hexadecimal number starts
with "0x" or "0X".  For example "0x1f" is decimal 31.  An octal number starts
with a zero.  "017" is decimal 15.  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 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 used for subtraction.  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 above, 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_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 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.  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 ".".  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 here: functions.

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 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:                                    string-functions
        nr2char()               get a character by its ASCII value
        char2nr()               get ASCII value of a character
        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
        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
        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
        strchars()              length of a string in characters
        strwidth()              size of string when displayed
        strdisplaywidth()       size of string when displayed, deals with tabs
        substitute()            substitute a pattern match with a string
        submatch()              get a specific match in ":s" and substitute()
        strpart()               get part of a string
        expand()                expand special keywords
        iconv()                 convert text from one encoding to another
        byteidx()               byte index of a character in a string
        byteidxcomp()           like byteidx() but count composing characters
        repeat()                repeat a string multiple times
        eval()                  evaluate a string expression

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
        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
        sort()                  sort a List
        reverse()               reverse the order of 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
        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

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
        filter()                remove selected entries from a Dictionary
        map()                   change each Dictionary entry
        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

Other computation:                                      bitwise-function
        and()                   bitwise AND
        invert()                bitwise invert
        or()                    bitwise OR
        xor()                   bitwise XOR
        sha256()                SHA-256 hash

Variables:                                              var-functions
        type()                  type of a variable
        islocked()              check if a variable is locked
        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
        getcurpos()             get position of the cursor
        getpos()                get position of cursor, mark, etc.
        setpos()                set position of cursor, mark, etc.
        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

Working with text in the current buffer:                text-functions
        getline()               get a line or list of lines from the buffer
        setline()               replace a line in the buffer
        append()                append line or list of lines in the buffer
        indent()                indent of a specific line
        cindent()               indent according to C indenting
        lispindent()            indent according to Lisp indenting
        nextnonblank()          find next non-blank line
        prevnonblank()          find previous non-blank line
        search()                find a match for a pattern
        searchpos()             find a match for a pattern
        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

                                        system-functions file-functions
System functions and manipulation of files:
        glob()                  expand wildcards
        globpath()              expand wildcards in a number of directories
        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
        getftype()              get the kind of a file
        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
        tempname()              get the name of a temporary file
        mkdir()                 create a new 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
        hostname()              name of the system
        readfile()              read a file into a List of lines
        writefile()             write a List of lines into a file

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

                        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
        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
        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
        bufwinnr()              get the window number of a specific buffer
        winbufnr()              get the buffer number of a specific window
        getbufline()            get a list of lines from the specified buffer

Command line:                                   command-line-functions
        getcmdline()            get the current command line
        getcmdpos()             get position of the cursor in the 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

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
        pumvisible()            check if the popup menu is displayed

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 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
        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
        getwinposx()            X position of the GUI Vim window
        getwinposy()            Y position of the GUI Vim window

Vim server:                                     server-functions
        serverlist()            return the list of server names
        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
        winrestcmd()            return command to restore window sizes
        winsaveview()           get view of current window
        winrestview()           restore saved view of current window

Mappings:                                   mapping-functions
        hasmapto()              check if a mapping exists
        mapcheck()              check if a matching mapping exists
        maparg()                get rhs of a mapping
        wildmenumode()          check if the wildmode is active

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
        cscope_connection()     check if a cscope connection exists
        did_filetype()          check if a FileType autocommand was used
        eventhandler()          check if invoked by an event handler
        getpid()                get process ID of Vim

        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

        getreg()                get contents of a register
        getregtype()            get type of a register
        setreg()                set contents and type of a register

        shiftwidth()            effective value of 'shiftwidth'

        taglist()               get list of matching tags
        tagfiles()              get a list of tags files

        luaeval()               evaluate Lua expression
        mzeval()                evaluate MzScheme expression
        py3eval()               evaluate Python expression (+python3)
        pyeval()                evaluate Python expression (+python)

==============================================================================
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.

==============================================================================
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': 'ein', 'two': 'zwei', 'three': 'drei'}
        :echo uk2de.translate('three one')
       drei ein 

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.

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 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.  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 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 <Bram@vim.org>

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 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: 

  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 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: 

 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 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: 

 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 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: 

 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".
        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 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: 

 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 <Bram@vim.org>
  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
help.txt local-additions.  The first "*" must be in the first column of the
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
"~/.vim/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
"~/.vim/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) 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 makes sure the function is only defined once: 

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


UNDO                                                    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.


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., ~/.vim/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.  However,
older Vim versions don't, thus your plugin should define it then.  This is an
example: 

  if exists(":CompilerSet") != 2
    command -nargs=* CompilerSet setlocal <args>
  endif
  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 ~/.vim/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 <Bram@vim.org>
        " 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:

        ~/.vim/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: http://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.

For utmost portability use Vim itself to pack scripts together.  This can be
done with the Vimball utility.  See vimball.

It's good if you add a line to allow automatic updating.  See glvs-plugins.

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

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