Nice approach. And my be merged with mine, e.g.:

#!/usr/bin/perl -l

use strict;
use warnings;

my @fh=map {
    open my $fh, '<', $_ or die "Can't open `$_': $!\n";
    $fh } @ARGV;

no warnings 'uninitialized';
print while $_=join '',
  map { chomp(my $line=<$_>); $line } @fh,

__END__
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However:

• you should s/undefined/uninitialized/;
• it may not be fully reliable if empty lines are to be expected in the files.

Update: the second point was a thinko as Zaxo pointed out.