use strict;
my $link1 = 'http://perlmonks.org/index.pl';
my $link2 = 'http://riverserver/dir1/dir2/index.html';
#more links etc...
$link1 =~ s/http\:\/\///;
$link2 =~ s/http\:\/\///;

my @link1 = split /\//, $link1;
my @link2 = split /\//, $link2;

print "$link1[0]\n";
print "$link2[0]\n";