To avoid puzzling problems with missing data files, test your input with something along these lines:

#!/usr/bin/perl
if (!defined $ARGV[0]) { # make sure some input is given
   die "No input file provided: $!";
} elsif (!-f $ARGV[0]) { # input is not a file
   die "Input $ARGV[0] not available as a file";
}
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Also suggested is the use of "use warnings" and "use strict" at the beginning of nearly every Perl program.