boo_radley's method will work for anything (provided you use a variable instead of a literal 'webpage3'), except that you probably shouldn't use a regexp match as he did and just use eq instead, in case they, for example, type in 'webpage' (boo_radley's would match, and thus not add, even though it's technically different). Depends on how you want to handle those cases, though.

#!/usr/bin/perl
use warnings;
use strict;

our @data = qw(webpage1 webpage2);

print "Webpage needed: ";      # <STDIN> flushes output buffers
chomp(my $response = <STDIN>); # <STDIN> instead of <> in case they
                               # add command line arguments

push @data, $response unless grep { $_ eq $response } @data;

print "$_\n" for @data;
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(Update: Expounded upon why eq should probably be used instead of m//)

bbfu
Black flowers blossum
Fearless on my breath
Teardrops on the fire
Fearless on my breath

push @data, $response unless grep { $_ eq $response } @data;
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Please advise, I understand now that the push function adds to end of list but why is the grep on the response needed?
Basically what is the grep { $_ eq $response } @data part doing??