Merge pull request #983 from borgified/fix_947

fixes #947 thank you @hanleilei

free-programming-books.md

@@ -1226,6 +1226,7 @@ See also [TeX](#tex)
 
 ###Perl
 * [Beginning Perl](http://www.perl.org/books/beginning-perl/)
+* [Data Munging with Perl](http://perlhacks.com/dmp.pdf) (PDF)
 * [Embedding Perl in HTML with Mason](http://www.masonbook.com/book/)
 * [Essential Perl](http://cslibrary.stanford.edu/108/EssentialPerl.pdf) (PDF)
 * [Exploring Programming Language Architecture in Perl](http://www.billhails.net/Book/)