Yet another way:

#!/usr/bin/perl -w
use strict;
use Getopt::Declare;
use vars '$range';
$range = 0;

my $opts = Getopt::Declare->new(<<'SPEC') || die <<USAGE;

    -ip <ip:s>          IP range [required]
                        {$range = $ip;}
    -file <infile:s>    get range from file [required]
                        {local @ARGV = $infile;chomp($range=<>)}
    <infile:s>          [ditto] 
                        [mutex: -file -ip <infile>]

SPEC
    $0 -file filename | -ip range | filename
USAGE

print $range,$/;
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