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How to get the exit status of a failed pipe in Bash

06/16/2017 • 2 minute read

The traditional method of accessing the exit status of a command in Bash is through the $? internal variable like so :

$ true
$ echo $?
0

But what if your first command fails and you pipe it to another command that will always succeed?

$ false
$ echo $?
1
$ false | tee log
$ echo $?
0

Thankfully, there are a few different ways to handle accessing the exit code for the correct command in the pipe.

Via $PIPESTATUS

The $PIPESTATUS array is made up of the exit status of each command in a pipe. Learn more on the Advanced Bash-Scripting Guide.

You can use:

$ false | tee log
$ echo "${PIPESTATUS[0]} ${PIPESTATUS[1]}"
1 0

You can also use ${PIPESTATUS[*]} or ${PIPESTATUS[@]}.

Note: $PIPESTATUS suffers from the usual issue of misbehaving when you pipe ls (which is why I never pipe ls when possible), so $PIPEFAIL may be a better option in those cases.

Via $PIPEFAIL

In Bash version 3 and beyond, you can use set -o pipefail to set the exit status to the status of the last failed command in a pipe instead of the last command in a pipe.

Via mispipe

The moreutils package includes a command named mispipe that has similar functionality to ${PIPESTATUS[0]}.

I don’t personally like installing extra software when I can just use Bash functionality, but not every user or OS has that option.

mispipe works by taking two arguments and returning the exit status of the first:

$ mispipe true false
$ echo $?
0

This has the advantage of only returning the exit status of the first command instead of triggering on any failure of the pipe sequence.

Conclusion

There are a variety of different ways to recover the exit status of a failed pipe in the sequence, and there are a lot more that I didn’t cover like creating your own named pipes with mkfifo or a tmp file with mktemp that stores the array of each exit status. These aren’t typically needed on a standard Linux/Bash install that you aren’t too worried about being POSIX compliant though.


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