Jezen Thomas

Jezen Thomas

CTO & Co-Founder at Supercede. Haskell programmer. Writing about business and software engineering. Working from anywhere.

Shell Script Static Analysis in Vim

I’m a big fan of static analysis for a few reasons:

  1. Enforcing a consistent style helps other developers quickly scan and understand the code I write.
  2. Some static analysis tools guide the programmer towards an approach that is more idiomatic of the language, which is a great way to learn.
  3. I’m only human and my clumsiness often causes bugs which at best slow me down, and otherwise potentially ruin my day. Code linting prevents this.

I also enjoy solving small problems with shell scripts, though the shell is a relatively unforgiving environment; you’re not given all the safety and sugar that you would have in Ruby, for example. Having some static analysis as part of my Bash script development workflow would make for an excellent first line of defence.

I have total confidence that any self-respecting IDE has some sort of static analysis built in for shell scripting, but I’m a Vim guy so that just wouldn’t be my cup of tea. All of this naturally pushes me in the direction of marrying Vim with ShellCheck, which (as I’m sure you’ve guessed) automatically detects problems with shell scripts and commands.

The first step is to install ShellCheck. If you’re running OSX like me, you can pull down a ready-to-go ShellCheck with Homebrew.

brew update && brew install shellcheck

The next step is to teach Vim to use ShellCheck as an external compiler. We can set this with makeprg. We’ll also want to ask ShellCheck to use gcc-style output, as Vim understands this by default. This could be added under an autocmd in your .vimrc, but instead I’m going to use Vim’s filetype plugin to store this configuration in its own file.

" ~/.vim/ftplugin/sh.vim
set makeprg=shellcheck\ -f\ gcc\ %
au BufWritePost * :silent make | redraw!

The second line of that snippet runs the :make command every time Vim writes to the shell script. We need to do the silent/redraw dance to suppress the “Hit ENTER to continue” prompt.

Finally, I’d prefer Vim to automatically open the quickfix window if ShellCheck found any problems with my shell script, so I add the following couple of lines to my ~/.vimrc.

au QuickFixCmdPost [^l]* nested cwindow
au QuickFixCmdPost    l* nested lwindow

Now, whenever I write to a shell script, Vim gives me immediate feedback so I can catch problems early. It’s worth noting also that ShellCheck reads in the shebang so you’ll receive information specific to the shell you choose.