should shellcheck warn *potential* SIGPIPE?

[e-kwsm]

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 a potential problem:

#!/bin/bash
set -eo pipefail
seq 100000 | head
echo unreachable

Here's what shellcheck currently says:

nothing.

Here's what I wanted to see:

-:3:14: warning: This may send SIGPIPE and abort execution

OK commands

• cat
• cut
• fold
• grep without -q etc
• od
• paste
• sha1sum etc
• shuf
• sort
• tac
• tail
• tr
• uniq

commands that may send SIGPIPE

• grep -q etc (pipefail and grep -q wont get along well #665; Add SC2337: warn about grep early exit in pipelines under pipefail #3498)
• head (warning against piping to head #429) → safe alternatives are sed -n -e '1,10p', sed -e '11,$d' or awk 'NR <= 10'

Of course SIGPIPE is not sent when the grep patten does not match or piped data is small enough (< 1 MiB).

commands that may send SIGPIPE (unclear)

• nawk—exit
• sed—q

It is hard to check awk and sed because it depends on the script bodies (and awk implementation):

seq 100000 |
  awk -f scriptfile
# ^~ This may send SIGPIPE and abort execution, depending on the script

and eventually

seq 100000 |
  unknown-command
# ^~ ShellCheck does not know this command and cannot guarantee that SIGPIPE will not sent

# if ShellCheck knows that the command does not read stdin, SC2216 will be issued