SC2242

exit "Bad filename"

echo "Bad filename" >&2
exit 1

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.

None