set -e makes function stop running early?

Question

I have a function that seems to break when I turn on errors with set -e. I suspect that it is working as intended but I can't see what I'm doing wrong.

Here is the function:

#!/usr/bin/env bash

set -e

my_function() {
    base_dir="/tmp/test"
    if [ ! -d $base_dir ]; then
        echo "Creating $base_dir"
        mkdir -p $base_dir
        touch $base_dir/some-file.txt
    fi

    is_edited=$(grep "foo" $base_dir/some-file.txt)

    if [ ! -z $is_edited  ]; then
        cd $base_dir
        echo "Doing stuff"
        docker run --rm debian ls
    fi

    echo
    echo "Done"
    echo
}

my_function

With set -e flipped on, the function returns seemingly without hit the echo statements. With set -e turned off, the echo statements get hit. What is happening and how do I fix this?

`grep` returns a non-zero exit code if it doesn't find a match. This will be treated as an error by `set -e`. — Barmar, Jan 16 '16 at 00:24
@Barmar Ah, that makes sense. Maybe there is a better approach to this than using grep or is there a better way to handle the return value for it? — jmreicha, Jan 16 '16 at 00:30

score 3 · Accepted Answer · answered Jan 16 '16 at 00:31

Try using:

is_edited=$(grep "foo" $base_dir/some-file.txt || test $? -eq 1)

The exit status of grep is 0 if it found a match, 1 if it didn't find a match, and 2 if it got an actual error. So if there's no match for foo in the file, it will be considered an error, and set -e will terminate the script. The above code translates 1 to a success, so the script will only terminate if grep gets a real error.

If you don't care about terminating the script if grep gets an error, you could just use

if grep -1 "foo" $base_dir/some-file.txt ; then
    ...
fi

The -q option makes it not print the matching line, just set its exit status based on whether it found a match.

score 1 · Answer 2 · answered Jan 16 '16 at 00:31

1

as fmtn07 stated, it's with the return code.

try changing the grep statement from:

is_edited=$(grep "foo" $base_dir/some-file.txt)

to:

is_edited=$(grep "foo" $base_dir/some-file.txt || true)

answered Jan 16 '16 at 00:31

yftse

183
6

This will prevent the script from aborting if `grep` really gets an error. – Barmar Jan 16 '16 at 00:31

set -e makes function stop running early?

2 Answers2