Automatically cancel binary execution when certain output is detected

Question

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?

Answer 1

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.

Answer 2

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'