Re: thread save calling an external command

[BrowserUk]

need to process the standard output and standard error.

Do you need them as separate streams? How are you processing them? Could you show the code where you are processing the output?

[Paul.Unix]

The idea is to have parallel processes running to avoid long running processes block processing other items. I am mainly interested in the error output of the external commands. The exit codes of the external command are not suitable to tell what went wrong.

[BrowserUk]

If you want both stdout and stderr (and don't mind them mixed together:

#! perl -slw
use strict;
use threads;

sub thread {
    my $output = '';
    open CMD, '-|', q[ perl -E"say( qq[$$:saying $_] ), warn( qq[$$:wa
+rning $_\n] ), sleep(1) for 1 .. 4" 2>&1 ] or die $!;
    $output .= $_ while <CMD>;
    close CMD;
    return $output;
}

printf "Got\n'%s'\n", $_->join for map threads->create( \&thread ), 1 
+.. 4;

__END__
C:\test>t-junk
Got
'33168:warning 1
33168:warning 2
33168:warning 3
33168:warning 4
33168:saying 1
33168:saying 2
33168:saying 3
33168:saying 4
'
Got
'30208:warning 1
30208:warning 2
30208:warning 3
30208:warning 4
30208:saying 1
30208:saying 2
30208:saying 3
30208:saying 4
'
Got
'15844:warning 1
15844:warning 2
15844:warning 3
15844:warning 4
15844:saying 1
15844:saying 2
15844:saying 3
15844:saying 4
'
Got
'15032:warning 1
15032:warning 2
15032:warning 3
15032:warning 4
15032:saying 1
15032:saying 2
15032:saying 3
15032:saying 4
'

If you only want stderr:

#! perl -slw
use strict;
use threads;

sub thread {
    my $output = '';
    open CMD, '-|', q[ perl -E"say( qq[$$:saying $_] ), warn( qq[$$:wa
+rning $_\n] ), sleep(1) for 1 .. 4" 2>&1 >nul ] or die $!;
    $output .= $_ while <CMD>;
    close CMD;
    return $output;
}

printf "Got\n'%s'\n", $_->join for map threads->create( \&thread ), 1 
+.. 4;

__END__
C:\test>t-junk
Got
'34456:warning 1
34456:warning 2
34456:warning 3
34456:warning 4
'
Got
'32700:warning 1
32700:warning 2
32700:warning 3
32700:warning 4
'
Got
'19172:warning 1
19172:warning 2
19172:warning 3
19172:warning 4
'
Got
'22176:warning 1
22176:warning 2
22176:warning 3
22176:warning 4
'

[Paul.Unix]

Thanks for this example. It got me going. I have chosen to use backticks while the thread has to wait on the completion of the external command. My conclusion, do not use IPC::Run3 or Capture::Tiny in multi threaded scripts.