You never declare or initialize $line_type in your code, which looks a bit suspicious, because you check for definedness of it.
To your question: You could just push the lines onto an array within the while loop.
Example:

#!perl
use strict;
use warnings;

my @lines;

for (qw/one two three/) {
   push @lines, $_;
   print "Found *** $_ *** $/";
}

print "Lines: ", join " - ", @lines;
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Hope this helped,
CombatSquirrel.

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Entropy is the tendency of everything going to hell.