#!/usr/bin/env perl -l

use strict;
use warnings;

use Getopt::Long 'GetOptionsFromString';

my ($x, $y, $z) = qw{42 fred 1.0};
my %opts = ('x=i', \$x, 'y=s', \$y, 'z=f', \$z);

print 'Option starting values:';
print "Options: x[$x] y[$y] z[$z]";

if (exists $ENV{USER_OPTS}) {
    GetOptionsFromString($ENV{USER_OPTS}, %opts);
    print 'After environment variable options processed:';
    print "Options: x[$x] y[$y] z[$z]";
}

if (@ARGV) {
    GetOptions(%opts);
    print 'After command line options processed:';
    print "Options: x[$x] y[$y] z[$z]";
}

##</code><code>##

$ pm_1196515_option_processing.pl
Option starting values:
Options: x[42] y[fred] z[1.0]

$ export USER_OPTS='-z 1.5'

$ pm_1196515_option_processing.pl
Option starting values:
Options: x[42] y[fred] z[1.0]
After environment variable options processed:
Options: x[42] y[fred] z[1.5]

$ pm_1196515_option_processing.pl -x 21
Option starting values:
Options: x[42] y[fred] z[1.0]
After environment variable options processed:
Options: x[42] y[fred] z[1.5]
After command line options processed:
Options: x[21] y[fred] z[1.5]

$ pm_1196515_option_processing.pl -y wilma -z 3.4
Option starting values:
Options: x[42] y[fred] z[1.0]
After environment variable options processed:
Options: x[42] y[fred] z[1.5]
After command line options processed:
Options: x[42] y[wilma] z[3.4]