Regular Expression: The Theory behind it!
When it comes to validating input regular expression becomes a very important part of your security plan. On a side note ensure your regular expressions are doing Acceptance-List approach and not a Deny-List approach to validation as mentioned in a previous blog.
Those use to writing a lot scripts have a very good understanding of regualar expressions and their are many others that find it challenging. I have discovered a twelve parts blog by Eric Lippert of Microsoft on the theory behind regular expression. For those that like to learn the theory behind regular expressions I highly recommend reading this. For those learning regular expression it may help to under the theory behind what you are learning.
- Regular Expression from Scratch, Part One: Defining Terms
- Regular Expression from Scratch, Part Two: Some Examples of Languages
- Regular Expression from Sratch, Part Three: Concatenation
- Regular Expression from Sratch, Part Four: The Kleene Closer of a Language
- Regular Expression from Sratch, Part Five: The Regular Expression Language
- Regular Expression from Sratch, Part Six: The Insanely Clever Bit
- Regular Expression from Sratch, Part Seven: Listing all Members of a Language in Order
- Regular Expression from Sratch, Part Eight: The Diagonal Argument
- Regular Expression from Sratch, Part Nine: A Dream of a Machine
- Regular Expression from Sratch, Part Ten: Magic
- Regular Expression from Sratch, Part Eleven: Eliminating Multi-Symbol Rules
- Regular Expression from Sratch, Part Twelve: Superpositions of States