# File: defect1.pl
use strict;
use warnings;

my $str = "  xyz";

$str =~ /^(\s*)/g or die;
print("match1: pos=", pos($str), "\n");

$str =~ /\G(\s*)/g or die;
print("match2: pos=", pos($str), "\n");

$str =~ /\G(\s*)/g or die;
print("match3: pos=", pos($str), "\n");

##</code><code>##

match1: pos=2
match2: pos=2
Died at defect1.pl line 13.

##</code><code>##

use strict;
use warnings;

my $str = "  xyz";
$str =~ /^(\s*)/g;
my ($x) = ($str =~ /\G(x)/g) or die;
defined(pos($str)) or warn("pos() is undefined!\n");
print("this should be x:$x\n");

##</code><code>##

pos() is undefined!
this should be x:x

##</code><code>##

use strict;
use warnings;

my $str = "  xyz";
$str =~ /^(\s*)/g;
my $x = ($str =~ /\G(x)/g)[0] or die;
defined(pos($str)) or warn("pos() is undefined!\n");
print("this should be x:$x\n");

##</code><code>##

pos() is undefined!
this should be x:x

##</code><code>##

use strict;
use warnings;

my $str = "  xyz";
$str =~ /^(\s*)/g;
$str =~ /\G(x)/g or die;
my $x = $1;
defined(pos($str)) or warn("pos() is undefined!\n");
print("this should be x:$x\n");

##</code><code>##

this should be x:x

##</code><code>##

This is perl 5, version 14, subversion 2 (v5.14.2) built for x86_64-linux-thread-multi