here we go

(update: please see Re: wiki regex reprocessing replacement (UPDATED^2) for better testcases including wrong markup)

use strict;
use warnings;
use Data::Dump qw/pp dd/;


use Test::More;

my $wiki =
    '_/one *two*/ three_ null _/four *five*/ six_  null _/seven *eight
+*/ nine_';

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



my $pre  = qr/(^|\s|>)/;
my $post = qr/($|\s|<)/;
my %h = (
    '*' => 'b' ,
    '/' => 'i' ,
    '_' => 'u' ,
);

    
sub tf { s{ $pre ([_*/]) (.*?) \2 (?=$post)}{$1<$h{$2}>$3</$h{$2}>}xg 
+};

$_=$wiki;

my $DBG = 1;

diag "IN <= '$wiki'\n\n" if $DBG;

for my $i (1..3) {
    tf();
    diag "$i: '$_'\n\n" if $DBG;
}



is($_,$expected," repeated replace works");

done_testing;
[download]

# IN <= '_/one *two*/ three_ null _/four *five*/ six_  null _/seven *e
+ight*/ nine_'
# 
# 1: '<u>/one *two*/ three</u> null <u>/four *five*/ six</u>  null <u>
+/seven *eight*/ nine</u>'
# 
# 2: '<u><i>one *two*</i> three</u> null <u><i>four *five*</i> six</u>
+  null <u><i>seven *eight*</i> nine</u>'
# 
# 3: '<u><i>one <b>two</b></i> three</u> null <u><i>four <b>five</b></
+i> six</u>  null <u><i>seven <b>eight</b></i> nine</u>'
# 
ok 1 -  repeated replace works
1..1
[download]

# IN <= '_/one *two*/ three_ null _/four *five*/ six_  null _/seven *eight*/ nine_'
# 
# 1: '/one *two*/ three null /four *five*/ six  null /seven *eight*/ nine'
# 
# 2: 'one *two* three null four *five* six  null seven *eight* nine'
# 
# 3: 'one two three null four five six  null seven eight nine'
# 
ok 1 -  repeated replace works
1..1