Vim autocmd based on file contents

Question

I'm trying to set up Vim to detect when a .tex file contains the command '\usepackage{sagemath}', and run a command accordingly. I've gotten to

:au BufReadPost,BufWritePost *.tex TTarget sagepdf

but that will fire for all .tex files, which isn't what I want.

Answer 1

Theres an example in my filetype.vim on how to destinguish html types. You can easily modify to suit your logic. Note the getline(n) =~ lines

" HTML (.shtml and .stm for server side)
au BufNewFile,BufRead *.html,*.htm,*.shtml,*.stm  call s:FThtml()

" Distinguish between HTML, XHTML and Django
fun! s:FThtml()
  let n = 1
  while n < 10 && n < line("$")
    if getline(n) =~ '\<DTD\s\+XHTML\s'
      setf xhtml
      return
    endif
    if getline(n) =~ '{%\s*\(extends\|block\)\>'
      setf html.django_template
"      setf htmldjango
      return
    endif
    let n = n + 1
  endwhile
  setf html
endfun

Answer 2

First, you should consider using a modeline.

If you can't get what you want with a modeline, you can use your own function in autocmd, like this:

function! MyFunction()
  ...
endfunction

autocmd BufReadPost,BufWritePost *.tex call MyFunction()

and you probably can write a function that checks whether a certain pattern matches, and then runs whatever you want.