feature request: detect wrong placement of /dev/null redirection

[Villemoes]

For bugs

• Rule Id (if any, e.g. SC1000):
• My shellcheck version (shellcheck --version or "online"):
• 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

• [ x] https://www.shellcheck.net/ (i.e. the latest commit) currently gives no useful warnings about this
• [ x] 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:

I managed to write something like this

#!/bin/sh
rmdir "/foo/bar" || true 2> /dev/null 

and only spotted the problem myself after the code was merged.

Here's what shellcheck currently says:

Nothing.

Here's what I wanted or expected to see:

Some warning about the /dev/null silencing being applied to a command that will never emit anything, and given the || true, was likely meant to be applied to the LHS command. So this is probably two feature requests (or easiest to do if considered like that): Output redirections applied to builtins like true, false, : are most likely useless, at least when the destination is also a known subject like /dev/null (true > file is not useless). And when a command is followed by || true , it is likely that any redirection of output applied to the RHS was meant to apply to the LHS.