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

use strict;

open my $graph, '<', '2211.txt' or
  die "Can't open `2211.txt': $!\n";

while (<GRAPH>)
{
        $a1 = push(@a1, $1);
        $a2 = push(@a2, $2);
    print @a1, @a2;
}

while (<GRAPH>)
{
...
        $a2 = $2;
        print $a1, $a2;
}

my (@a1, @a2);
while (<GRAPH>)
...
        push @a2, $2;
}
print @a1, @a2;