#!/usr/bin/perl

my $xml = "<root>\n\t<element attribute='foo'>\n\t\t<!-- -->\n\t</element>\n\t<element attribute='bar'>\n\t\t<!-- -->\n\t</element>\n</root>";
print "before:\n";
print $xml, $/;

my $node = "\t<element attribute='new'>\n\t</element>\n";
print $node, $/;

my $name='foo';
$xml =~ s!\t<element attribute='$name'>.*</element>\n!$node!se;

print "after:\n";
print $xml, $/;