Ask HN: How do I get started with regular expressions?

Thus, I have tinkered with code only on an as-needed basis, when I have had very specific problems that I knew a computer could do for me accurately and quickly – changing file names in a folder, performing repetitive editorial tasks, automatically filing downloaded sources with specific names. Most of these things were done in Applescript, and they are all good things for me, because the time they save me gets devoted to thinking that helps me build a case better. I can't hire an intern, because that's expensive, but my meager Applescripting I have done so far has made for a very reliable intern.

Recently, I wanted to write a script that would scan my documents, identify local currency figures, convert them to a global standard ($, €, or Bitcoin), and then insert them into my report copy. This seemed very reasonable to me, and I thought that it would be easy (since everything else I had done had been a simple matter of articulating the problem and finding the solution somewhere online). Time consuming, perhaps, but easy... like reading, copying, pasting, and then tinkering to customize it.

This was not easy.

Someone has suggested I try regular expressions to solve the problem. The thing is, that sentence doesn't mean anything to me, because I don't know where/how to begin, and I don't really know what regex is.

Where would you send someone like me to start learning regex?

Cheers, -s

http://regex.learncodethehardway.org/book/

[1] http://en.wikipedia.org/wiki/Regular_expression

After you understand the basics, you can follow these steps that I use every time I need to program regular expressions.

1) Google a chart explaining the regular expression syntax for the language you are using (something like - applesscript regexp chart)

2) Create some test code to help refine your regular expression. Your code should have

* a - REGEX STRING - the regular expression value you are testing. You can store this value in a variable in your code, reference this value from a text file, or input it manually every time you run your script. I like to give myself access to this outside the code, so for a webpage have a form with an input field with this value. For scripting languages, make this a parameter of your script, so you can play with it quickly without having to change any code.

* b - STRING DATA - this is the value (or values) you will be comparing your regular expression against. You can store this in a variable, or reference this from a text file. Try and think of all cases that could potentially cause your script to break. For example, the currency symbols you are trying to replace, could they ever be used in ways where you would not want to replace them?

* c - RESULTS - you should output the results every time you run your script and keep tweaking it until you are satisfied with the output.

3) Implement your awesome REGEX in your code.