Feature: Should warn about unquoted exports in /bin/sh

[koalaman]

For new checks and feature suggestions

• shellcheck.net (i.e. the latest commit) currently gives no useful warnings about this
• I searched through https://github.com/koalaman/shellcheck/issues and didn't find anything related

Here's a snippet or screenshot that shows the problem:

#!/bin/sh
var="foo bar"
export foo=$var

Here's what shellcheck currently says:

Nothing

Here's what I wanted or expected to see:

The value for export must be quoted in POSIX sh

[mklement0]

Excellent idea; if the author of /etc/profile.d/apps-bin-path.sh that ships with Ubuntu 18.04 had been warned about this, PowerShell/PowerShell#12020 wouldn't have happened.

[emorrp1]

This is also relevant to SC2046 for command substitution assignments, and interacts with SC2155, here's a few additional examples:

#!/bin/sh
var=$(cat) # does *not* need quoting
export var=$(cat) # SC2155
if var=$(cat); then
  true
fi