SC2319 - confusing warning message when checking $? after [[ ]]

[aslatter]

For bugs

• Rule Id (if any, e.g. SC1000): SC2319
• My shellcheck version (shellcheck --version or "online"): v0.8.0-45-gd1d574c
• The rule's wiki page does not already cover this (e.g. https://shellcheck.net/wiki/SC2086)
• I tried on https://www.shellcheck.net/ and verified that this is still a problem on the latest commit - (not really, but "--version" indicates I am using the current commit)

For new checks and feature suggestions

• https://www.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/bash

[[ -n "${DB_HOST:-}" && -n "${DB_TOKEN:-}" && -n "${DISTRO:-}" ]]
should_check_db=$?

echo "$should_check_db"

Here's what shellcheck currently says:

In /work/test.sh line 4:
should_check_db=$?
                ^-- SC2319 (warning): This $? refers to a condition, not a command. Assign to a variable to avoid it being overwritten.

For more information:
  https://www.shellcheck.net/wiki/SC2319 -- This $? refers to a condition, no...

Here's what I wanted or expected to see:

It's confusing that shellcheck is telling me to assign $? to a variable on the line where I assign $? to a variable.

It's not clear why I shouldn't be checking the exit-code of "[[]]" - that's the whole point of "[[]]". None of the "problematic code" examples in the wiki look like the code I have, also.

Better descriptions or examples around why this construction is problematic would be helpful.

[koalaman]

Agreed, your pattern was listed under "Exceptions". However, the check has now been updated to exclude cases where the $? is used unconditionally (like your case or [ -d test ]; return $?). Thanks for testing on the git branch!

[aslatter]

Thanks for the fix! The change works great.

[mgmsam]

Hi all!!

Conducted a test on the site https://www.shellcheck.net
I report that this problem is repeated inside a function:

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

#!/bin/bash
print_codout() {
	RETURN=$?
	printf '%s\n' "$RETURN"
}
[ -f foo ] || print_codout

Here's what shellcheck currently says:

$ shellcheck myscript

Line 3
RETURN=$?
       ^-- SC2319 (warning): This $? refers to a condition, not a command. Assign to a variable to avoid it being overwritten.