Use open to open a file handle then use:

while (<IN>) {
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to scan the file. Use index or a regular expression match to skip (using next) until the interface line is found. Skip until the description line is found:

/^description/ && last while <IN>;

my $description = $_;
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Process the description then use the same technique for the rest of the lines you need to match.

/^description/ && last while <IN>;

that confused the heck out of me! how about this form?

    $_ = <IN> until /^description/;
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doh!

Because that tests $_ before the first value is assigned to it and doesn't terminate for a file that doesn't include a matching line!

---

DWIM is Perl's answer to Gödel

use strict;
use warnings;
use Data::Dumper;

my %hash = ();
{
local $/ = "interface ";
while(<DATA>) {
    my ($key) = /description\s+(.*)/;
    next if $key =~ /^\s*$/;
    my ($value) = /switchport trunk allowed vlan\s*(.*)/;
    $hash{$key} = $value;
}

print Dumper \%hash;

__DATA__
.....
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