PHP

Regular Expression Documentaion

Regular Expressions are super powerful, and are included in most programming languages.
Regardless of what programming language you use, regular expressions will make certain text processing tasks a breeze.
If you have ever looped through every character in a string of text searching for specific characters just stop and learn regular expressions.
You will be so glad you did.

Perl

http://perldoc.perl.org/perlrequick.html

Search Drupal User Profiles

It is difficult to search for users (in code) based on profile information in Drupal 6 due to the flexible nature in which the profiles module stores information. Basically profiles are stored in 2 tables.
mysql> select * from profile_fields;
+-----+------------+-------------------+-------------+---------------------+------+-----------+--------+----------+----------+------------+--------------+---------+
| fid | title      | name              | explanation | category            | page | type      | weight | required | register | visibility | autocomplete | options |