Recipe 22.2. Matching Words

22.2.1. Problem

You want to pull out all words from a string.

22.2.2. Solution

The key to this is carefully defining what you mean by a word. Once you've created your definition, use the special character types to create your regular expression:

/\S+/         // everything that isn't whitespace /[A-Z'-]+/i   // all upper and lowercase letters, apostrophes, and hyphens

22.2.3. Discussion

The simple question "What is a word?" is surprisingly complicated. While the Perl-compatible regular expressions have a built-in word character type, specified by \w, it's important to understand exactly how PHP defines a word. Otherwise, your results may not be what you expect.

Normally, because it comes directly from Perl's definition of a word, \w encompasses all letters, digits, and underscores; this means a_z is a word, but the email address is not.

In this recipe, we only consider English words, but other languages use different alphabets. Because Perl-compatible regular expressions use the current locale to define its settings, altering the locale can switch the definition of a letter, which then redefines the meaning of a word.

To combat this, you may want to explicitly enumerate the characters belonging to your words inside a character class. To add a nonstandard character, use \xdd, where dd is a character's hex code.

22.2.4. See Also

Recipe 19.2 for information about setting locales and 19.13 for information about using UTF-8-encoded strings with the PCRE regex functions.

PHP Cookbook, 2nd Edition
PHP Cookbook: Solutions and Examples for PHP Programmers
ISBN: 0596101015
EAN: 2147483647
Year: 2006
Pages: 445

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