For example, (.) is a subpattern that matches any character, just like. Subpatterns are simply any regular expression enclosed by parenthesis. This can be a little tricky to wrap your head around when encountered for the first time, so we start with some simple contrived examples to give you some practice. Regular expressions really begin to show their power when we use subpatterns and replace patterns. You can use parenthesis to enclose alternations if you need to also match stuff before and/or after the alternation. Now figure out what the ^ and $ positional assertions and the alternation patterns mean. What is the difference between * and *? or + and +? When would you use the greedy and non-greedy versions? There is another repetition pattern which means match at least n occurrences. Now try the Repetition patterns *, *?, +, +? and ?. Also experiment with creating your own class search patterns - for example, what would a class to match DNA nucleotide symbols look like?
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Feel free to edit the text to include new words or numbers if you are curious as to how they will be matched. What does it match? Repeat for all the Wildcards to get a good intuition of what each wildcard matches. Next try \s in the Find box and click Next. Keep clicking Next - you will see that the. in the Find box and click Next to see what matches. On page 45, there is a table of Wildcards.
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If at any point you get confused over the next few paragraphs, look at the examples from page 47-49 for concrete illustrations of how to use regular expressions. The Grep option tells TextWrangler that we are using regular expressions, and wrap around that we want to do search and replace on the whole document regardless of where our cursor/insertion point is. Open the Find dialog and check the Grep and Wrap around boxes. We’ll continue with the cats and dogs file just to get comfortable with the basic elements of regular expressions. You have already come across regular expressions in the Unix session - now you will see how to use them to manipulate text files. We now come to the main part of this session, which is how to use regular expressions (or regex) for text manipulation described in pages 44 to 51 of the TextWrangler tutorial.
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