Just read and print the first line?

#!/usr/bin/perl

use strict;
use warnings;

while (my $line = <DATA>){
    next if $line =~ /Port/;
    print "$line\n";
    last;
}


__DATA__
RNC               RIP-IP     Switch /Router     Port
GURRNC1     172.16.1.2     GURSW1             1/6
GURRNC1     172.16.2.2     GURSW2             2/6
GURRNC2     172.16.3.2     GURSW3       3/6
GURRNC2     172.16.4.2     GURSW4             4/6
[download]

Output:

$ ./line.pl 
GURRNC1     172.16.1.2     GURSW1             1/6
[download]

Now simply replace <DATA> with a real file handle. Hopefully this will be enough to get you on the right track. Your question is awfly vague though so it's difficult to know exactly what you need.

-stevieb