use strict;
use warnings;

my %Recs;
my $pc_name;

while (<DATA>) 
{
    if (/interface (\S+)$/) {
        $pc_name = $1;
        $Recs{$pc_name} = {};   # Create record.
        next;
    }

    if (/switchport description (.*)$/) {
        $Recs{$pc_name}{description} = $1;
        next;
    }
}

for $pc_name (keys %Recs)
{
    my $description = $Recs{$pc_name}{description};
    if (defined $description) {
        $description = "switchport description $description";
    } else {
        $description = "";
    }
    print("interface $pc_name = switchport description $description\n");
}

##</code><code>##

use strict;
use warnings;

my %descriptions;
my $pc_name;

while (<DATA>) 
{
    if (/interface (\S+)$/) {
        $pc_name = $1;
        $descriptions{$pc_name} = undef;
        next;
    }

    if (/switchport description (.*)$/) {
        $descriptions{$pc_name} = $1;
        next;
    }
}

for $pc_name (keys %descriptions)
{
    my $description = $descriptions{$pc_name};
    if (defined $description) {
        $description = "switchport description $description";
    } else {
        $description = "";
    }
    print("interface $pc_name = switchport description $description\n");
}