Consider adding a linter / some static analysis

[dwijnand]

Here's a collection of useful resources I've held on to for this:

• https://github.com/koalaman/shellcheck
• http://redsymbol.net/articles/unofficial-bash-strict-mode/
• http://blog.pangyanhan.com/posts/2015-12-25-on-the-unofficial-bash-strict-mode-by-aaron-maxwell.html

These would also have to be wired into Travis.

[dwijnand]

• http://jvns.ca/blog/2017/03/26/bash-quirks/

[dwijnand]

ghcup runs shellcheck like so:

edo()
{
	printf "\\033[0;34m%s\\033[0m\\n" "$*" 1>&2
    "$@" || exit 2
}

# install shellcheck
edo wget https://storage.googleapis.com/shellcheck/shellcheck-latest.linux.x86_64.tar.xz
edo tar -xJf shellcheck-latest.linux.x86_64.tar.xz
edo mv shellcheck-latest/shellcheck "$HOME"/.local/bin/shellcheck

# check our script for errors
edo shellcheck ghcup