How to substitute pipe dependent on the previous command exit code?

Asked Sep 28 '17 at 17:15

Active Sep 28 '17 at 17:15

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I have following line in the script:

maim -s | tee $fname > last.png

maim -s takes screenshot and returns 0 if it was taken succesfully or 1 if it was cancelled. The problem is, if it returns 0, it pipes zero bytes anyway so after cancelling i have two empty files $fname and last.png.

I want to redirect output to /dev/null if maim -s returns 0 right on the place, without writing to temporary file and copying it to $fname and last.png if it isn't empty.
How do I do that?

asked Sep 28 '17 at 17:15

fedoraman

All commands in a pipeline run in parallel. Because they're started at the same time, the second one can't possibly know if the first one succeeded. – Charles Duffy Sep 28 '17 at 17:17
BTW, consider *renaming* rather than *copying* -- that's an atomic operation. – Charles Duffy Sep 28 '17 at 17:18
dam, that's right... so, only temporary file then? – fedoraman Sep 28 '17 at 17:19
You need to buffer somewhere -- either a temporary file or in memory. – Charles Duffy Sep 28 '17 at 17:19

How to substitute pipe dependent on the previous command exit code?

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