use strict;
use warnings;

my $system = 'something';
my %vlan;

# --- Lines Omitted ---

my $vl_number = 1;

while( <STDIN> ) {
    chomp;
    $vlan{ 'VLAN' . $vl_number++ } = $_;
}

# --- Lines Omitted ---
while( my ( $key, $value ) = each %vlan ) {
    print "Now checking: $system\_$key $value\n";
}