grep 'gateway' infile > outfile

##</code><code>##

perl -ne'print if /gateway/' infile > outfile

##</code><code>##

perl -ne"print if /gateway/" infile > outfile

##</code><code>##

# Usage: script.pl infile outfile
# or
# Usage: perl script.pl infile outfile

use strict;
use warnings;

my ($qfn_in, $qfn_out) = @ARGV;

open(my $fh_in, '<', $qfn_in)
   or die("Unable to read file \"$qfn_in\": $!\n");

open(my $fh_out, '>', $qfn_out)
   or die("Unable to create file \"$qfn_out\": $!\n");

while (<$fh_in>) {
   if (/gateway/) {
      print $fh_out $_;
   }
}