Autocommands for Matlab in vim?

I use several different programming languages every day, and I'd like to have different tab widths (in spaces) for each. For example: I use the "standard" 2 spaces for Ruby, but all our existing Matlab code uses 4 spaces.

I have this from my personal ~/.vimrc:

augroup lang_perl
    au!
    set 开发者_开发技巧tabstop=4 " tabstop length N in spaces
    set shiftwidth=4 " make >> and friends (<<, ^T, ^D) shift N, not the default 8
    set expandtab " Use spaces instead of tabs
augroup END

augroup lang_ruby
    au!
    set tabstop=2 " tabstop length N in spaces
    set shiftwidth=2 " make >> and friends (<<, ^T, ^D) shift N, not the default 8
    set expandtab " Use spaces instead of tabs
augroup END

Those work, but the following doesn't:

augroup lang_matlab
    au!
    set tabstop=4 " tabstop length N in spaces
    set shiftwidth=4 " make >> and friends (<<, ^T, ^D) shift N, not the default 8
    set expandtab " Use spaces instead of tabs
augroup END

I really don't understand how augroup lang_ruby figures out that I'm editing a Ruby file. (My searches brought up ftdetect, but the solution wasn't obvious.) It doesn't seem like vim knows that I'm editing Matlab using augroup lang_matlab. What do I change to make this work?

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If you want to have a large number of settings for {filetype}, you should put them into ~/.vim/ftplugin/{filetype}.vim or into file that matches ~/.vim/ftplugin/{filetype}/**/*.vim (examples: ~/.vim/ftplugin/ruby/foo.vim, ~/.vim/ftplugin/ruby/foo/bar.vim). In this case you don't need any autocommands at all. If you still want to use autocommands, use the following:

augroup lang_matlab
    autocmd!
    autocmd FileType matlab      setlocal ts=4 sw=4 et
augroup END

. Note two things: FileType event (it is there and it is not BufRead,BufNewFile) and setlocal instead of plain set. First is intended to be used for filetype settings, second is how buffer-specific options must be set.

About why perl and ruby settings work and why matlab settings does not: your example code is just the same as

augroup lang_perl
    autocmd!
augroup END
augroup lang_ruby
    autocmd!
augroup END

set tabstop=4 " tabstop length N in spaces
set shiftwidth=4 " make >> and friends (<<, ^T, ^D) shift N, not the default 8
set expandtab " Use spaces instead of tabs

set tabstop=2 " tabstop length N in spaces
set shiftwidth=2 " make >> and friends (<<, ^T, ^D) shift N, not the default 8
set expandtab " Use spaces instead of tabs

So, you effectively set ts=2 sw=2 et. But the $VIMRUNTIME/ftplugin/perl.vim contains the following code:

setlocal  tabstop=4
setlocal  shiftwidth=4

so, ts=4 sw=4 for perl is set into ftplugin/perl.vim, not in your vimrc (if you have installed perl-support plugin). You can check it by replacing tabstop=4 with tabstop=8 in vimrc.

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I cannot tell you how it's determined that lang_perl or lang_ruby shall be read. But looking at the autocommand documentation brings up an example for gzipped files (:he gzip-example):

augroup gzip
  autocmd!
  autocmd BufReadPre,FileReadPre       *.gz set bin
  autocmd BufReadPost,FileReadPost     *.gz '[,']!gunzip
  autocmd BufReadPost,FileReadPost     *.gz set nobin
  autocmd BufReadPost,FileReadPost     *.gz execute ":doautocmd BufReadPost " . expand("%:r")
  autocmd BufWritePost,FileWritePost   *.gz !mv <afile> <afile>:r
  autocmd BufWritePost,FileWritePost   *.gz !gzip <afile>:r
  autocmd FileAppendPre                *.gz !gunzip <afile>
  autocmd FileAppendPre                *.gz !mv <afile>:r <afile>
  autocmd FileAppendPost               *.gz !mv <afile> <afile>:r
  autocmd FileAppendPost               *.gz !gzip <afile>:r
augroup END

See it? Every autocmd that gets specified carries an Event (BufReadPre, FileReadPre) and the extension for which it shall be executed (*.gz). This is backing up my hitherto opinion that you can use any name for your augroup but have to specify an extension that the augroup shall be responsible for in order to get it working correctly.

Another quote of :he autocmd-groups:

Normally, when executing autocommands automatically, Vim uses the autocommands for all groups. The group only matters when executing autocommands with ":doautocmd" or ":doautoall", or when defining or deleting autocommands.

So, in order to make an augroup for matlab files, this one should do the trick:

augroup lang_matlab
  autocmd!
  autocmd BufRead       *.m set ts=4 sw=4 expandtab
augroup END

And make sure that these settings don't get overwritten by any augroups that do something unconditional (i.e. modify the other augroup definitions too).

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Use ftplugins, configuring vim will be much more easier to achieve. See gVim and multiple programming languages