use strict;
my $pattern = 'ip address';
open IN_FILE, '<', 'some_file' or die $!;
open OUT_FILE, '>', 'some_other_file' or die $!;
while(my $line = <FILE>){
  print OUT_FILE $line;
  print OUT_FILE $line if $line =~ /^$pattern/;
}
close(IN_FILE);
close(OUT_FILE);