my $str = "  xyz"
print "$str\n";

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

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

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

##</code><code>##

  xyz
match1: pos=2
  xyz
0 0
2 2
match2: pos=2
  xyz
2 2
2 2
Warning: something's wrong at /tmp/Perl-1.pl line 20.
Use of uninitialized value in print at /tmp/Perl-1.pl line 21.
match3: pos=
  xyz
2 2
2 2