$str = "(<citationref linkend=\" cit314-1 cit314-2 cit314-3 cit314-4 cit314-5\"/>)";
if( $str =~ s/<ref links=\"(.*?)\"(.*?)\/>/<ref links=\"$1\"$2>(?{ &getString($1) })<\/ref>/ ){
	print "Match was found." . "\n";
}
print $str . "\n";

sub getString($s){	
	my $s = shift;
	...more processing of $s...
	return $s;
}