my $module = 'xyz abc';

open my $PIPE, '-|', 'ps', '-aef' or die "Cannot open pipe from 'ps' $!";

my $pid;
while ( <$PIPE> ) {
    next unless /$module/;
    $pid = ( split )[ 2 ];
    }

close $PIPE or warn $! ? "Error closing 'ps' pipe: $!"
                       : "Exit status $? from 'ps'";