If by "number" you mean an integer device number, the following technique for getting a list of results for regex captures should help. It is documented among other places here: http://perldoc.perl.org/perlrequick.html#Extracting-matches

use warnings;
use strict;

my ($device) = defined($ARGV[0]) ? $ARGV[0] =~ /^\s*(\d+)\s*$/ : '';
print "Device #$device\n";
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