On the Debuggable blog, Felix Geisendorfer shows how to create a string parser that allows you to pull out parts of the string you don't currently want manipulated to be put back later.

If you've ever written any non-trivial String processing code, you've probably ran into the situation where you wanted to exclude certain parts of your string for a certain operation. Usually that would mean you have to tokenize your string, or adjust the operation you want to run so it doesn't affect the part of the string you want to exclude from it. Both of those solutions can be fairly time intensive so I was looking for a shortcut and found one.

He provides the code for this string substitution class, a method substitute() that matches based on a regular expression and, if found, stores the parts for later use.

From the PHP-Coding_Practices.com site, Tim Koschuetzki has posted an interesting suggestion for developers working with long expressions to make thing simpler - substituting temporary variables for portions of the expression.

Introduce Explaining Variable is particularly useful with long if-statements. You can take each condition, introduce an explaining variable and the conditional logic will read very well. Another occasion is a long algorithm where each step in the calculation can be explained with a well-named temporary variable.

The method is basically the following - declare the temporary variable with part of the expression, replace where needed in the expression, repeat for other parts of the expression. In his example code, he demonstrates its use, pulling out portions of an equation to calculate an item's price to make it much more readable.