This will use ShellCheck to check for common shell scripting errors in
the project. If any errors or oddness is detected, it will give a
warning (which may be ignored).

http://www.shellcheck.net/

Shell scripting problems may be permanently ignored by adding a comment
line above the offending line, like:
   # shellcheck disable=SC2016
   PKG_NAME=$(autoconf --trace 'AC_INIT:$1' configure.ac)

The linter is currently implemented using Arcanist’s script-and-regex
linter, which means it is quite limited. All messages are outputted as
warnings, and it has to invoke file beforehand to work out whether a
file is actually a shell script. The return value of the command should
always be 0 otherwise script-and-regex will abort; hence the `|| true`.

https://secure.phabricator.com/book/phabricator/article/arcanist_lint_script_and_regex/

In particular, the script-and-regex configuration needs to use a hack in
the regex to set the ‘warning’ regex capture grou...