use strict;
my $str = '<chapter id="chap1">
<para0><title></title></para0>
</chapter>
<chapter id="chap2"> <title>THEORY</title>
<section id="Thoery">
<title>theory Section</title>
<para0 verstatus="ver">
<title>Theory Para 0 </title>
<text>blah blah</text>
</para0>
</section>
<section id="Next section">
<title>title</title>
<para0>
<title>Title</title>
<text>blah blah</text>
</para0>
</section>
<section id="More sections">
<title>title</title>
<para0>
<title>Title</title>
<text>blah blah</text>
</para0>
</section>
<section id="section">
<title>title</title>
<para0>
<title>Title</title>
<text>blah blah</text>
</para0>
</section>';
my $regex = qr/(<section[a-z="'\s]+>([\s\S]*?)<\/section>)/mip;
my $subst = '$1';
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