Here's an idea 
$_ = q~<bl>List item 1
List item 2
<bl>List item a
List item b
List item c</bl>
List item 3</bl>
~;

s~</?bl>~~g;
s~(List.+?)$~<listitem>$1</listitem>~gm;

print $_,$/;

__END__
<listitem>List item 1</listitem>
<listitem>List item 2</listitem>
<listitem>List item a</listitem>
<listitem>List item b</listitem>
<listitem>List item c</listitem>
<listitem>List item 3</listitem>

[download]

In reply to Re: Help in using Regular Expressions by Anonymous Monk
in thread Help in using Regular Expressions by rsriram

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
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