43Using 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.

    Table of contents

  1. Plugins for a filetype
  2. Adding a filetype

43.1Plugins for a filetype

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:

  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.

  1. 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.

43.2Adding 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 “Autocommands”.) 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.