#!/usr/bin/perl

use strict;
use warnings;

my $dummy = "";
my $rollup = combine("");
my $oneline;

while (<DATA>) {
    $rollup->($_);

    # once end is reached store it in a variable    
    # reset variable-in-sub for next iteration
    if (/end;/) {
        # breaks if I remove $dummy and replace it with ""
        $oneline = $rollup->($dummy);
        $rollup = combine("");
        print $oneline,$/;
    }
}


sub combine {
    my $concat = shift;
    return sub {
        chomp($_[0]);
        $concat .= $_[0];
        return ($concat);
    }
}


##</code><code>##

__DATA__
line1;
line2;
line3;
end;
line4;
line5;
end;


##</code><code>##

line1;line2;line3;end;
line4;line5;end;


##</code><code>##

Modification of a read-only value attempted at closure line 26, <DATA> line 4.