CODEWITHSUNDEEP
perlioperl-io
RobEarl
RobEarl

Reputation: 7912

Monitoring external process: Exit when STDOUT matches pattern

I'm running a system command and waiting for output matching a specific pattern, e.g:

open(my $fh, '-|', 'echo line 1; sleep 20; echo line 2');
while (<$fh>) {
    print && last if /1/;
}
close $fh;

This will print line 1 and leave the loop but won't exit until the external command has completed.

How can I allow the script to exit immediately after matching the required output?

Upvotes: 3

Views: 152

Answers (3)

RobEarl
RobEarl

Reputation: 7912

If the process is to be left running after the match is found, append an & to the command to run it in the background:

open(my $fh, '-|', 'echo line 1 && sleep 20 && echo line 2 &');
while (<$fh>) {
    print && last if /1/;
}
close $fh;

Upvotes: -1

Mark Setchell
Mark Setchell

Reputation: 207465

You could use awk:

echo hello; sleep 2; echo pattern |awk '{print}/pattern/{exit}'

This will give you all the lines till pattern occurs, then exit.

Upvotes: 0

mpapec
mpapec

Reputation: 50647

You can send TERM signal to the PID and then close file handle without waiting,

my $pid = open(my $fh, '-|', 'echo line 1;sleep 5; echo line 2') or die $!;
while (<$fh>) {
    print && last if /1/;
}
kill TERM => $pid;
close $fh;

Upvotes: 3

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