SC2320 (warning): This $? refers to echo/printf, not a previous command.

[macalixx]

For bugs

• Rule Id: SC2320
• My shellcheck version: 0.9.0
• 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

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

echo "hola" >> /tmp/prueba
Codigo=$?

echo $Codigo

Here's what shellcheck currently says:

Codigo=$?
       ^-- [SC2320](https://www.shellcheck.net/wiki/SC2320) (warning): This $? refers to echo/printf, not a previous command. Assign to variable to avoid it being overwritten.

Here's what I wanted or expected to see:

An "echo" redirected to a file is a file write operation. It is necessary to obtain the exit code of that operation, because writing to a file will fail due to lack of permissions, and sometimes it is necessary to verify it.

Wiki says:

If you intentionally refer to echo to get the result of a write, you can ignore this message. Alternatively, write it out as in if echo $$ > "$pidfile"; then status=0; else status=1; fi

But, I think that a report should be as clean as possible, and I think it is easy to detect these cases so as not to show warnings.

[brother]

Intention is very hard to catch.
I would assume that this is a common error in the wild and that's the reason for having the warning to begin with. And if found it is easy to ignore with a directive as suggested in the wiki.

A patch for making the discovery more robust and to avoid some of these fasle positives is as always welcome.