use strict;
use warnings;

my ( @IPS, $IP );

print "Enter name:\n";
my $s = <>;
chomp $s;

open my $fh, '<', 'routers.txt' or die $!;
while ( my $line = <$fh> ) {

    if ( $line =~ /\b$s\b/ ) {
        my ($IP) = $line =~ /(\d+\.\d+\.\d+\.\d+)/;
        push( @IPS, $IP );
    }

}

close $fh;

print "$_\n" for @IPS;