perl usage()和getopt

#!/usr/bin/perl
#perl search.pl --infile Targets.Lung.Carcinoma.genelist.txt --homogene Homo_sapiens.gene_info --outfile Targets.Lung.Carcinoma.geneID.txt
use warnings;
use strict;
use Getopt::Long;

my ($infile,$homogene,$outfile);
GetOptions('infile=s'=>$infile,'homogene=s'=>$homogene,'outfile=s'=>$outfile,"help|h" =>&USAGE,)or USAGE();

sub USAGE {
my $usage=<<"USAGE";
USAGE:
$0
--infile input filefiel

--homogene Homo_sapiens.gene_info

--outfile output file

USAGE
print $usage;
exit;
}