use strict;
my $str = 'D01A42F5-FD89-4c8f-8065-726AD4363411';
my $regex = qr/([0-9A-F])([0-9A-F])([0-9A-F])([0-9A-F])([0-9A-F])([0-9A-F])([0-9A-F])([0-9A-F])\-([0-9A-F])([0-9A-F])([0-9A-F])([0-9A-F])\-4([0-9A-F])([0-9A-F])([0-9A-F])\-([0-9A-F])([0-9A-F])([0-9A-F])([0-9A-F])\-([0-9A-F])([0-9A-F])([0-9A-F])([0-9A-F])([0-9A-F])([0-9A-F])([0-9A-F])([0-9A-F])([0-9A-F])([0-9A-F])([0-9A-F])([0-9A-F])/mip;
my $subst = '$31$1$30$2$29$3$28$4-$27$5$26$6-4$25$7$24-$8$23$9$22-$10$21$11$20$12$19$13$18$14$17$15$16';
my $result = $str =~ s/$regex/$subst/rg;
print "The result of the substitution is' $result\n";
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html