Check grep return code

Question

My script contains following sets in place:

set -o errexit
set -o pipefail
set -o nounset

Now I would like o grep (not sed, awk, etc) for letter A in file b, and add the result to the file c:

grep A b >> C

The problem is that grep exits with RC 1 if no A is found in b file, which in my case is fine as I don't see that as an issue. In that case I wrapped grep command in a function and run:

function func_1() {
  grep A b >> C
}

if func_1; then
  echo "OK"
else
  echo "STILL OK"
end

Everything works great, but soon I realised it would be nice to catch RC=2 (grep failure). How can I do that?

Answer 1

I don't see how that protects you from the effects of set -e

I think you'll need need a wrapper function that disables errexit for the duration, something like:

function func_2 {
    set +o errexit
    func_1 "$@"
    rc=$?
    set -o errexit
    echo "$rc"
}

case $(func_2) in
    0) echo "success" ;;
    1) echo "not found" ;;
    2) echo "trouble in grep-land" ;; 
esac

---

Reading closely the documentation for set -e, you can handle commands with non-zero exit status in certain situations. However, you function cannot return a non-zero exit status:

#!/bin/bash
set -o errexit

function mygrep {
    local rc=0
    # on the left side of ||, errexit not triggered
    grep "$@" >/dev/null || rc=$?
#     return $rc         # nope, will trigger errexit
    echo $rc
}

echo "test 1: exit status 0"
mygrep $USER /etc/passwd

echo "test 2: exit status 1"
mygrep foobarbaz /etc/passwd

echo "test 2: exit status 2"
mygrep $USER /file_does_not_exist

echo done

outputs

test 1: exit status 0
0
test 2: exit status 1
1
test 2: exit status 2
grep: /file_does_not_exist: No such file or directory
2
done