Having a good grasp of regular expressions is a necessary prerequisite to working with mod_rewrite. All too often, people try to build regular expressions by the brute-force method, trying various different combinations at random until something seems to mostly work. This results in expressions that are inefficient and fragile, as well as being a great waste of time and the cause of much frustration.
Keep a bookmark in this chapter, and refer back to it when you’re trying to figure out what a particular regex is doing.
Other recommended reference sources include the Perl regular expression documentation, which you can find online at http://perldoc.perl.org/perlre.html or by typing perldoc perlre at your command line, and the PCRE documentation, which you can find online at http://pcre.org/pcre.txt.
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