And a Perl solution that does the same: 
use File::Slurp;

my @a1 = sort {$a cmp $b} read_file shift;
my @a2 = sort {$a cmp $b} read_file shift; 

while (@a1 && @a2) {
    my $cmp = $a1[0] cmp $a2[0];
    print $a1[0] if !$cmp;
    shift @a1 if $cmp <= 0;
    shift @a2 if $cmp >= 0;
}

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In reply to Re^2: problem while reading multiple files by JavaFan
in thread problem while reading multiple files by rajyalakshmi

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