#!/usr/bin/perl

# usage:
#   myscript *.txt
#   myscript `ls *.txt`
#   ls *.txt | myscript

use strict;
use warnings;

my @files = @ARGV;

if (!-t STDIN) {
   while (<STDIN>) {
      chomp;
      push @files, $_;
   }
}

...

##</code><code>##

#!/usr/bin/perl

# usage:
#   myscript *.txt
#   myscript `ls *.txt`

use strict;
use warnings;

my @files = @ARGV;

...