SC2242 – ShellCheck Wiki

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Can only exit with status 0-255. Other data should be written to stdout/stderr.

Problematic code:

exit "Bad filename"

Correct code:

echo "Bad filename" >&2
exit 1

Rationale:

exit can only be used to signal success or failure (0 = success, 1-255 = failure). It can not be used to return string data, and it can not be used to print error messages.

String data should be written stdout, before an exit 0 to exit with success.

Errors should instead be written to stderr, with an exit 1 (or higher) to exit with failure:

if [ ! -f "$1" ]
then
   echo "$1 is not a regular file" >&2
   exit 1
fi

Note in particular that exit -1 is equivalent to exit 255, but that exit 1 is the more canonical way of expressing the first possible error code.

Exceptions:

None

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