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Greg Dubicki
Asked: 2016-09-09 03:49:09 +0800 CST

Normal shell vs subshell vs "bash -c" last command exit code

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I am trying to get the exit code of the last command chained with && and || correctly.

I encountered a strange behavior that I cannot explain. Please help.

This is my exit-code.sh test script:

#!/bin/bash
echo "running exit-code with $1"
exit $1

This works as expected:

$ ./exit-code.sh 1 && ./exit-code.sh 2 && ./exit-code.sh 3 || echo last exit code: $?
running exit-code with 1
last command exit code: 1

The same with () to run it in a subshell:

$ (./exit-code.sh 1 && ./exit-code.sh 2 && ./exit-code.sh 3 || echo last exit code: $?)
running exit-code with 1
last exit code: 1

But:

$ /bin/bash -c "./exit-code.sh 1 && ./exit-code.sh 2 && ./exit-code.sh 3 || echo last exit code: $?"
running exit-code with 1
last exit code: 0

Why do I get exit code 0 here?

bash shell

2 Answers

  1. Best Answer

    Why do I get exit code 0 here?

    The reason is that with the double quotes, parameter expansion (of the special parameter, $?) is carried out before passing arguments to the new Bash process. If you turn on debug and verbose mode, you can see this clearly:

    $ set -xv
$ bash -c "(./exit-code.sh 1 && ./exit-code.sh 2 && ./exit-code.sh 3 || echo last exit code: $?)"
bash -c "(./exit-code.sh 1 && ./exit-code.sh 2 && ./exit-code.sh 3 || echo last exit code: $?)"
+ bash -c '(./exit-code.sh 1 && ./exit-code.sh 2 && ./exit-code.sh 3 || echo last exit code: 0)'
running exit-code with 1
last exit code: 0
$ set +xv

    In this case $? is set to 0 because the previous command (set -xv in this example) executed successfully.

    • 4

  2. Quotes

    Just use single ' quotes

    /bin/bash -c './exit-code.sh 1 && ./exit-code.sh 2 && ./exit-code.sh 3 || echo last exit code: $?'

running exit-code with 1
last exit code: 1
    • 3