#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11112988
use warnings;

my $wiki =
    '_/one *two*/ th/ree_ null _/four *five*/ six_  null _/se_ven *eig
+ht*/ nine_';

my $expected =
    '<u><i>one <b>two</b></i> th/ree</u> null <u><i>four <b>five</b></
+i> six</u>  null <u><i>se_ven <b>eight</b></i> nine</u>'; 

my %h = (
    '*' => 'b' ,
    '/' => 'i' ,
    '_' => 'u' ,
);

my $html = $wiki =~ s{ (?:^|\s) \K ([*_/]+) | ([*_/]*) (?=$|\s) }
  { $1 ? $1 =~ s|.|<$h{$&}>|gr : $2 =~ s|.|</$h{$&}>|gr }gexr;

print $html eq $expected ? "passed" : "FAILED", "\n\n";
print $wiki, "\n\n", $expected, "\n\n", $html, "\n";
[download]

Outputs;

passed

_/one *two*/ th/ree_ null _/four *five*/ six_  null _/se_ven *eight*/ 
+nine_

<u><i>one <b>two</b></i> th/ree</u> null <u><i>four <b>five</b></i> si
+x</u>  null <u><i>se_ven <b>eight</b></i> nine</u>

<u><i>one <b>two</b></i> th/ree</u> null <u><i>four <b>five</b></i> si
+x</u>  null <u><i>se_ven <b>eight</b></i> nine</u>
[download]

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.