#!perl

use strict;
use warnings;

my ($INFILE, $OUTFILE);

open $INFILE, 'acis_empx20_win32d_3400.log' or die "Cannot open file: $!";
open $OUTFILE, '> acis_filtered.log' or die "Cannot open acis_filtered.log: $!";

while(my $line = <$INFILE>)
{
	if($line =~ /RS/)
		{ print $OUTFILE $line }
}

close $INFILE;
close $OUTFILE;


and example of use: C:>script.pl