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3 Regular Expressions

A regular expression, or regexp, is a way of describing a set of strings. Because regular expressions are such a fundamental part of awk programming, their format and use deserve a separate chapter.

A regular expression enclosed in slashes (‘/’) is an awk pattern that matches every input record whose text belongs to that set. The simplest regular expression is a sequence of letters, numbers, or both. Such a regexp matches any string that contains that sequence. Thus, the regexp ‘foo’ matches any string containing ‘foo’. Thus, the pattern /foo/ matches any input record containing the three adjacent characters ‘fooanywhere in the record. Other kinds of regexps let you specify more complicated classes of strings.

Initially, the examples in this chapter are simple. As we explain more about how regular expressions work, we present more complicated instances.

Regexp Usage    How to Use Regular Expressions.
Escape Sequences    How to write nonprinting characters.
Regexp Operators    Regular Expression Operators.
Bracket Expressions    What can go between ‘[...]’.
Leftmost Longest    How much text matches.
Computed Regexps    Using Dynamic Regexps.
GNU Regexp Operators    Operators specific to GNU software.
Case-sensitivity    How to do case-insensitive matching.
Regexp Summary    Regular expressions summary.

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