Limit on number of pipes after long-running command?


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# 8  
No, that's not the issue: xinput test 6 definitely outputs to stdout. Proof is that xinput test 6 6>/dev/null produces output, but xinput test 6 1>/dev/null produces no output.

As I tried to explain, 6 in the command is an argument to xinput that tells it the input device I'm interested in testing. It is not a file descriptor.

Last edited by DevuanFan; 05-16-2019 at 12:31 PM..
# 9  
Might be due to buffering. Try as a zeroth approximation
Code:
xinput test 6 | awk -Winteractive '{print $3}'

This User Gave Thanks to RudiC For This Post:
# 10  
Both gawk and nawk complain: option `-W interactive` unrecognized, ignored.

But I think we're getting warmer. It does seem to have something to do with buffering.
# 11  
Quote:
Originally Posted by DevuanFan
Both gawk and nawk complain: option `-W interactive` unrecognized, ignored.

But I think we're getting warmer. It does seem to have something to do with buffering.
how about:
Code:
xinput test 6 | gawk '{print $3;fflush()}' | grep whatEver

# 12  
YES! That works. Is there a way to generalize this solution (e.g., at the level of the shell), so that things keep flowing down the pipe?

--- Post updated at 04:09 PM ---

Thank you, RudiC and vgersh99. It was a buffering issue. I found this helpful thread:
shell - Turn off buffering in pipe - Unix & Linux Stack Exchange

I can confirm that either of these pipelines work as expected:
Code:
stdbuf -o0 xinput test 9 | stdbuf -o0 grep release | awk '{print $3}'

Code:
unbuffer xinput test 9 | unbuffer -p grep release | awk '{print $3}'

This User Gave Thanks to DevuanFan For This Post:
# 13  
Quote:
Originally Posted by DevuanFan
YES! That works. Is there a way to generalize this solution (e.g., at the level of the shell), so that things keep flowing down the pipe?

--- Post updated at 04:09 PM ---

Thank you, RudiC and vgersh99. It was a buffering issue. I found this helpful thread:
shell - Turn off buffering in pipe - Unix & Linux Stack Exchange

I can confirm that either of these pipelines work as expected:
Code:
stdbuf -o0 xinput test 9 | stdbuf -o0 grep release | awk '{print $3}'

Code:
unbuffer xinput test 9 | unbuffer -p grep release | awk '{print $3}'

That's exactly the same thread I found Googling: Turn off buffering in pipe.
It's a combo of stdbuf/unbuffer/cat/script - multiple suggestions.
# 14  
Actually, for some reason it is not necessary to turn off buffering in the first command. Only in the second. In other words, these versions also work:

Code:
xinput test 9 | stdbuf -o0 grep release | awk '{print $3}'

Code:
xinput test 9 | unbuffer -p grep release | awk '{print $3}'

Guess I need to read up on buffering, since I'm stoked that we found a fix but don't fully understand why we don't have to unbuffer the first command.
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