Fix ShellCheck errors in our shell code base

Originally created by @intrigeri on #17675 (Redmine)

pabs privately submitted a series of patches that fix ShellCheck errors.

IMO it’s great to get closer to established coding best practices and style guides, and perhaps at some point we can even enforce some basic rules via pre-merge gatekeeper CI. In passing, related effort for our Ruby code: #17646 (closed).

Message-ID: <42d3f2b8c52c1164e841862570b13dc9735c4b05.camel@bonedaddy.net>

Related issues

Related to #17646 (closed)

Edited May 15, 2020 by intrigeri

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information