Prepending statement with a ! operator is a common way to avoid errexit on a particular command.
SC2251 currently correctly warns that the the return code might not be checked. There is an exception to the rule where $? is checked afterwards. The problem is that the value of $? is inverted by the ! operator and it converts all the non-zero return codes to 0. One often needs to check the explicit return value of the original statement and a common way to do it is to check ${PIPESTATUS[0]} instead.
Consider for example the following common snippet (intended to check if getopt can be used on the system):
#!/bin/bash
set -o errexit -o pipefail -o noclobber -o nounset
# -allow a command to fail with !’s side effect on errexit
# -use return value from ${PIPESTATUS[0]}, because ! hosed $?
! getopt --test > /dev/null
if [[ ${PIPESTATUS[0]} -ne 4 ]]; then
echo "I’m sorry, 'getopt --test' failed in this environment." >&2
exit 1
fi
I suggest that checking ${PIPESTATUS[0]} could be considered equivalent to checking the $? and might be safely added to exceptions to this rule (SC2251)
fedy-cz
commented
6 months ago
Prepending statement with a
!operator is a common way to avoid errexit on a particular command.SC2251 currently correctly warns that the the return code might not be checked. There is an exception to the rule where
$?is checked afterwards. The problem is that the value of$?is inverted by the!operator and it converts all the non-zero return codes to 0. One often needs to check the explicit return value of the original statement and a common way to do it is to check${PIPESTATUS[0]}instead.Consider for example the following common snippet (intended to check if getopt can be used on the system):
I suggest that checking
${PIPESTATUS[0]}could be considered equivalent to checking the$?and might be safely added to exceptions to this rule (SC2251)