In Chapter 6, you learned basic Unix commands and how they work. Now you'll build on that knowledge and expand your command library. This chapter tackles advanced commands and regular expressions (formulas for matching strings that follow specific patterns). Regular expressions are important, and they're also quite challenging when you're just learning about them. Don't worry, though, because this chapter provides a good foundation for your learning.
A regular expression is a syntactical set or phrase that represents a pattern of text or strings. Regular expressions enable you to represent a varying array of characters with a much smaller set of predefined characters. They often include metacharacters—characters that represent another set or group of characters or commands.
No discussion of regular expressions and metacharacters is useful without examples, so create a file called /tmp/testfile that you can use as you work your way through this chapter: Here's what to put in the file (note the capitalization and punctuation):
Juliet Capulet The model identifier is DEn5c89zt. Sarcastic was what he was. No, he was just sarcastic. Simplicity The quick brown fox jumps over the lazy dog It's a Cello? Not a Violin? This character is (*) is the splat in Unix. activity apricot capulet cat celebration corporation cot cut cutting
dc9tg4 eclectic housecat persnickety The punctuation and capitalization is important in this example. simplicity ...