Is it possible to somehow run an executable through the shell and automatically make it stop executing the moment a specific string is matched/detected in the output? Just as if i would hit CTRL+C, manually?
If yes, how?
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2 Answers
use a coprocess:
coproc CO { yourcommand; }
while read -ru ${CO[0]} line
do
case "$line" in
*somestring*) kill $CO_PID; break ;;
esac
done
Note that if the command buffers its output, as many commands do when writing to a pipe, there will be some delay before the string is detected.
2 Comments
SQRCAT
I don't find any
coproc binary on my system. I'm on Mac OSX, should have included that in my question though.
Barmar
It's not a binary, it's built into bash 4.x. Unfortunately, OS X has bash 3.x. If you google bash coprocesses, you can find out how to do the same thing using named pipes.
You could use awk:
program | awk '/pattern/{exit}1'
If you also want to print the line containing the pattern, say:
program | awk '/pattern/{print;exit}1'
For example:
$ seq 200 | awk '/9/{print;exit}1'
1
2
3
4
5
6
7
8
9
EDIT: (With reference to your comment, whether the program would stop or not.) Following is a script that would execute in an infinite loop:
n=1
while : ; do
echo $n
n=$((n+1))
sleep 1
done
This script foo.sh was executed by saying:
$ time bash foo.sh | awk '/9/{print;exit}1'
1
2
3
4
5
6
7
8
9
real 0m9.097s
user 0m0.011s
sys 0m0.011s
As you can see, the script terminated when the pattern was detected in the output.
EDIT: It seems that your program buffers the output. You could use stdbuf:
stdbuf -o0 yourprogram | awk '/pattern/{print;exit}1'
If you're using mawk, then say:
stdbuf -o0 yourprogram | mawk -W interactive '/pattern/{print;exit}1'
7 Comments
SQRCAT
It seems that using this, the program is still having to finish. It takes as long as if i call it without awk. Is this possible?
devnull
@SquareCat No, the program should finish.
awk would send a SIGPIPE to the program which should terminate it. See the edit above for a demo.
tripleee
If the program produces output slowly, it could run for a while before the
SIGPIPE is generated, though.devnull
@tripleee Good thought, I'll suggest using
stdbuf.devnull
@SquareCat It seems that the output is buffered; the edit above might work for you.
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