Linux in a Nutshell, Fifth Edition

697

This is the Title of the Book, eMatter Edition

Copyright © 2006 O’Reilly & Associates, Inc. All rights reserved.

Chapter 7

7

Pattern Matching

A number of Linux text-processing utilities let you search for, and in some cases

change, text patterns rather than fixed strings. These utilities include the editing

programs ed, ex, vi, and sed; the gawk programming language; and the

commands grep and egrep. Text patterns (called regular expressions in computer

science literature) contain normal characters mixed with special characters (called

metacharacters).

This chapter presents the following topics:

• Filenames versus patterns

• Description of metacharacters

• List of metacharacters available to each program

• Examples

For more information on regular expressions, see the O’Reilly book Mastering

Regular Expressions.

Filenames Versus Patterns

Metacharacters used in pattern matching are different from metacharacters used

for filename expansion (see Chapter 6). However, several metacharacters have

meaning for both regular expressions and for filename expansion. This can lead to

a problem: the shell sees the command line first, and can potentially interpret an

unquoted regular expression metacharacter as a filename expansion. For example,

the command:

$ grep [A-Z]* chap[12]

could be transformed by the shell into:

$ grep Array.c Bug.c Comp.c chap1 chap2