# Vim documentation: usr_43

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    *usr_43.txt*	For Vim version 8.1.  Last change: 2015 Oct 23

    		     VIM USER MANUAL - by Bram Moolenaar

    			       Using filetypes

    When you are editing a file of a certain type, for example a C program or a
    shell script, you often use the same option settings and mappings.  You
    quickly get tired of manually setting these each time.  This chapter explains
    how to do it automatically.

    |43.1|	Plugins for a filetype
    |43.2|	Adding a filetype

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

    *43.1*	Plugins for a filetype				*filetype-plugin*

    How to start using filetype plugins has already been discussed here:
    |add-filetype-plugin|.  But you probably are not satisfied with the default
    settings, because they have been kept minimal.  Suppose that for C files you
    want to set the 'softtabstop' option to 4 and define a mapping to insert a
    three-line comment.  You do this with only two steps:

    							*your-runtime-dir*
    1. Create your own runtime directory.  On Unix this usually is "~/.vim".  In
       this directory create the "ftplugin" directory:

    	mkdir ~/.vim
    	mkdir ~/.vim/ftplugin

       When you are not on Unix, check the value of the 'runtimepath' option to
       see where Vim will look for the "ftplugin" directory:

    	set runtimepath

       You would normally use the first directory name (before the first comma).
       You might want to prepend a directory name to the 'runtimepath' option in
       your |vimrc| file if you don't like the default value.

    2. Create the file "~/.vim/ftplugin/c.vim", with the contents:

    	setlocal softtabstop=4
    	noremap <buffer> <LocalLeader>c o/**************<CR><CR>/<Esc>
    	let b:undo_ftplugin = "setl softtabstop< | unmap <buffer> <LocalLeader>c"

    Try editing a C file.  You should notice that the 'softtabstop' option is set
    to 4.  But when you edit another file it's reset to the default zero.  That is
    because the ":setlocal" command was used.  This sets the 'softtabstop' option
    only locally to the buffer.  As soon as you edit another buffer, it will be
    set to the value set for that buffer.  For a new buffer it will get the
    default value or the value from the last ":set" command.

    Likewise, the mapping for "\c" will disappear when editing another buffer.
    The ":map <buffer>" command creates a mapping that is local to the current
    buffer.  This works with any mapping command: ":map!", ":vmap", etc.  The
    |<LocalLeader>| in the mapping is replaced with the value of the
    "maplocalleader" variable.

    The line to set b:undo_ftplugin is for when the filetype is set to another
    value.  In that case you will want to undo your preferences.  The
    b:undo_ftplugin variable is executed as a command. Watch out for characters
    with a special meaning inside a string, such as a backslash.

    You can find examples for filetype plugins in this directory:

    	$VIMRUNTIME/ftplugin/

    More details about writing a filetype plugin can be found here:
    |write-plugin|.

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

    *43.2*	Adding a filetype

    If you are using a type of file that is not recognized by Vim, this is how to
    get it recognized.  You need a runtime directory of your own.  See
    |your-runtime-dir| above.

    Create a file "filetype.vim" which contains an autocommand for your filetype.
    (Autocommands were explained in section |40.3|.)  Example:

    	augroup filetypedetect
    	au BufNewFile,BufRead *.xyz	setf xyz
    	augroup END

    This will recognize all files that end in ".xyz" as the "xyz" filetype.  The
    ":augroup" commands put this autocommand in the "filetypedetect" group.  This
    allows removing all autocommands for filetype detection when doing ":filetype
    off".  The "setf" command will set the 'filetype' option to its argument,
    unless it was set already.  This will make sure that 'filetype' isn't set
    twice.

    You can use many different patterns to match the name of your file.  Directory
    names can also be included.  See |autocmd-patterns|.  For example, the files
    under "/usr/share/scripts/" are all "ruby" files, but don't have the expected
    file name extension.  Adding this to the example above:

    	augroup filetypedetect
    	au BufNewFile,BufRead *.xyz			setf xyz
    	au BufNewFile,BufRead /usr/share/scripts/*	setf ruby
    	augroup END

    However, if you now edit a file /usr/share/scripts/README.txt, this is not a
    ruby file.  The danger of a pattern ending in "*" is that it quickly matches
    too many files.  To avoid trouble with this, put the filetype.vim file in
    another directory, one that is at the end of 'runtimepath'.  For Unix for
    example, you could use "~/.vim/after/filetype.vim".
       You now put the detection of text files in ~/.vim/filetype.vim:

    	augroup filetypedetect
    	au BufNewFile,BufRead *.txt			setf text
    	augroup END

    That file is found in 'runtimepath' first.  Then use this in
    ~/.vim/after/filetype.vim, which is found last:

    	augroup filetypedetect
    	au BufNewFile,BufRead /usr/share/scripts/*	setf ruby
    	augroup END

    What will happen now is that Vim searches for "filetype.vim" files in each
    directory in 'runtimepath'.  First ~/.vim/filetype.vim is found.  The
    autocommand to catch *.txt files is defined there.  Then Vim finds the
    filetype.vim file in $VIMRUNTIME, which is halfway 'runtimepath'.  Finally
    ~/.vim/after/filetype.vim is found and the autocommand for detecting ruby
    files in /usr/share/scripts is added.
       When you now edit /usr/share/scripts/README.txt, the autocommands are
    checked in the order in which they were defined.  The *.txt pattern matches,
    thus "setf text" is executed to set the filetype to "text".  The pattern for
    ruby matches too, and the "setf ruby" is executed.  But since 'filetype' was
    already set to "text", nothing happens here.
       When you edit the file /usr/share/scripts/foobar the same autocommands are
    checked.  Only the one for ruby matches and "setf ruby" sets 'filetype' to
    ruby.

    RECOGNIZING BY CONTENTS

    If your file cannot be recognized by its file name, you might be able to
    recognize it by its contents.  For example, many script files start with a
    line like:

    	#!/bin/xyz

    To recognize this script create a file "scripts.vim" in your runtime directory
    (same place where filetype.vim goes).  It might look like this:

    	if did_filetype()
    	  finish
    	endif
    	if getline(1) =~ '^#!.*[/\\]xyz\>'
    	  setf xyz
    	endif

    The first check with did_filetype() is to avoid that you will check the
    contents of files for which the filetype was already detected by the file
    name.  That avoids wasting time on checking the file when the "setf" command
    won't do anything.
       The scripts.vim file is sourced by an autocommand in the default
    filetype.vim file.  Therefore, the order of checks is:

    	1. filetype.vim files before $VIMRUNTIME in 'runtimepath'
    	2. first part of $VIMRUNTIME/filetype.vim
    	3. all scripts.vim files in 'runtimepath'
    	4. remainder of $VIMRUNTIME/filetype.vim
    	5. filetype.vim files after $VIMRUNTIME in 'runtimepath'

    If this is not sufficient for you, add an autocommand that matches all files
    and sources a script or executes a function to check the contents of the file.

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

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