Regular Expressions (Pattern Matching) (Unix Power Tools, 3rd Edition)
Chapter 32. Regular Expressions (Pattern Matching)
Contents:
That's an Expression
Don't Confuse Regular Expressions with Wildcards
Understanding Expressions
Using Metacharacters in Regular Expressions
Regular Expressions: The Anchor Characters ^ and $
Regular Expressions: Matching a Character with a Character Set
Regular Expressions: Match Any Character with . (Dot)
Regular Expressions: Specifying a Range of Characters with [...]
Regular Expressions: Exceptions in a Character Set
Regular Expressions: Repeating Character Sets with *
Regular Expressions: Matching a Specific Number of Sets with \ { and \ }
Regular Expressions: Matching Words with \ < and \ >
Regular Expressions: Remembering Patterns with \ (, \ ), and \1
Regular Expressions: Potential Problems
Extended Regular Expressions
Getting Regular Expressions Right
Just What Does a Regular Expression Match?
Limiting the Extent of a Match
I Never Meta Character I Didn't Like
Valid Metacharacters for Different Unix Programs
Pattern Matching Quick Reference with Examples
32.1. That's an Expression
When my young daughter is struggling to
understand the meaning of an idiomatic expression, such as,
"Someone let the cat out of the
bag," before I tell her what it means, I have to
tell her that it's
an
expression, that she's not to
interpret it literally. (As a consequence, she also uses
"That's just an
expression" to qualify her own remarks, especially
when she is unsure about what she has just said.)
An expression, even in computer terminology, is not something to be
interpreted literally. It is something that needs to be evaluated.
Many Unix programs use a special "regular expression
syntax" for specifying what you could think of as
"wildcard searches" through files.
Regular expressions describe
patterns, or sequences of characters,
without necessarily specifying the characters literally.
You'll also hear this process referred to as
" pattern matching."
In this chapter, we depart a bit from the usual
"tips and tricks" style of the book
to provide an extended tutorial about regular expressions that starts
in Section 32.4. We did this because regular
expressions are so important to many of the tips and tricks elsewhere
in the book, and we wanted to make sure that they are covered
thoroughly.
This tutorial article is accompanied by a few snippets of advice
(Section 32.16 and Section 32.18) and a few tools that help you see what your
expressions are matching (Section 32.17).
There's also a quick reference (Section 32.21) for those of you who just need a refresher.
For tips, tricks, and tools that rely on an understanding of regular
expression syntax, you have only to look at:
Chapter 13
Chapter 17
Chapter 20
Chapter 34
Chapter 41
O'Reilly's Mastering
Regular Expressions, by Jeffrey Friedl, is a gold mine of
examples and specifics.
--DD and TOR
31.13. Automatic Setup When You Enter/Exit a Directory32.2. Don't Confuse Regular Expressions with Wildcards
Copyright © 2003 O'Reilly & Associates. All rights reserved.
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