If you create lots of scripts, you can arrange for the executable bit to be automagically set on save if the file begins with '#!/usr/bin/' or '#!/bin'.

function! MySetExecutableIfScript(line1, current_file)
  if a:line1 =~ '^#!\(/usr\)*/bin/'
    let chmod_command = "silent !chmod ugo+x " . a:current_file
    execute chmod_command
  endif
endfunction
autocmd BufWritePost * call MySetExecutableIfScript(getline(1), expand("%:p"))

CommentsEdit

WARNING: autocommands with constructs like 'if condition | clause | endif' are problematic for me, and apparently for others given the comments below. They seem to have the potential to make other autocommands declared later not happen. I recommend having you autocommand call a function and doing your ifing in there as above.

Here's something a little better for Python:

" Python header
function! <SID>PythonHeader()
  call setline(1, "#! /bin/sh")
  call append(1, "# vim: filetype=python")
  call append(2, "\"\"\":\"")
  call append(3, "exec python $0 ${1+\"$@\"}")
  call append(4, "\"\"\"")
  call append(5, "")
  exe 6
endfunction
au BufEnter *.py if getline(1) == "" | call s:PythonHeader() | endif

Or for shell:

" Shell header
function! <SID>ShellHeader()
  call setline(1, "#! /bin/sh")
  call append(1, "")
  exe 2
endfunction
au BufEnter *.sh if getline(1) == "" | call s:ShellHeader() | endif

I did not want the script to keep doing the chmod even when the file is already excutable, so this is what I have in my vimrc:

" Define a function that can tell me if a file is executable
function! FileExecutable (fname)
  execute "silent! ! test -x" a:fname
  return v:shell_error
endfunction
" Automatically make Perl and Shell scripts executable if they aren't already
au BufWritePost *.sh,*.pl,*.cgi if FileExecutable("%:p") | :!chmod a+x % ^@ endif

Note that the ^@ is actually Ctrl-V Ctrl-J (an embedded new line), because you cannot use | as a separator after an external command.

For the problem with " | endif" after a shell command - e.g.:

au BufWritePost * if getline(1) =~ "^#! ?/bin/[a-z]*sh" | silent !chmod a+x <afile> | endif

I noticed that the above works fine for csh / tcsh, but not in a bash shell. I got this to work fine for a bash shell:

au BufWritePost * if getline(1) =~ "^#! ?/bin/[a-z]*sh" | silent !chmod a+x <afile>
au BufWritePost * | endif