use strict;
use warnings;

# See perlvar for why $/ = "" causes $record to contain your entire record at once. The point is to read your data record-at-a-time instead of line-at-a-time.
local $/ = "";
while ( my $record = <DATA> ) {

    # See perlre for why (.+) fetches everything on the same line as the text being matched but doesn't continue onto the next line. Remember, $record is a multi-line string.
    my ( $pc_name ) = $record =~ /interface (.+)/;
    my ( $switch_name ) = $record =~ /switchport description (.+)/;

    print "$pc_name: $switch_name\n";
}