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Comments on How to invert command exit code?

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How to invert command exit code?

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How to apply a logical not to a shell command, e.g. in a Bash script?

So if the command exited with 0 (success) I would like it to be changed to a non-zero value, and if it exited with a non-zero value (failure) like 1, I would like it to become 0. A negation of sorts.

shell shell-scripting
posted about 1 year ago
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Iizuki‭
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An exclamation mark followed by space in the beginning of a pipeline will negate the final exit code of the pipeline.

Here's an example in Bash. Echoing $? will print out the exit code of the previous command (which is also an echo in this case).

$ echo OpenStreetMap is the best map
OpenStreetMap is the best map
$ echo $?
0
$ ! echo OpenStreetMap is meh
OpenStreetMap is meh
$ echo $?
1

This is a Posix thing.

posted about 1 year ago
8mo ago
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Iizuki‭
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Why emphasize "final"? (3 comments)
Why emphasize "final"?
Karl Knechtel‭ wrote 8 months ago
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Are return codes for intermediate steps in the pipeline relevant and/or accessible in the first place?

Michael‭ wrote 8 months ago
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Makes sense to me. It could save some poor sod from thinking you could pipe to test like this:

false | test || echo 'False!'
! false | test && echo 'True!'

You're inverting the exit code of test, not inverting false as someone might imagine. (Is this contrived? Yes, very. Is it important? Maybe.)

Kamil Maciorowski‭ wrote 7 months ago
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Karl Knechtel‭ "accessible in the first place?" – In Bash there is ${PIPESTATUS[@]}, it is not affected by the ! the answer is about. You can think of $? as derived from ${PIPESTATUS[@]} according to pipefail (set -o | grep pipefail) and the presence (or not) of !.