Regular Expressions Cookbook

5.2. Find Any of Multiple Words

Problem

You want to find any one out of a list of words, without having to search through the subject string multiple times.

Solution

Using alternation

The simple solution is to alternate between the words you want to match:

\b(?:one|two|three)\b

Regex options: Case insensitive

Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

More complicated examples of matching similar words are shown in Recipe 5.3.

Example JavaScript solution

var subject = 'One times two plus one equals three.';

var regex = /\b(?:one|two|three)\b/gi;

subject.match(regex);
// returns an array with four matches: ['One','two','one','three']

// This function does the same thing but accepts an array of words to
// match. Any regex metacharacters within the accepted words are escaped
// with a backslash before searching.

function match_words (subject, words) {
    var regex_metachars = /[(){}[\]*+?.\\^$|,\-]/g;

    for (var i = 0; i < words.length; i++) {
        words[i] = words[i].replace(regex_metachars, '\\$&');
    }

    var regex = new RegExp('\\b(?:' + words.join('|') + ')\\b', 'gi');

    return subject.match(regex) || [];
}

match_words(subject, ['one','two','three']);
// returns an array with four matches: ['One','two','one','three']

Discussion

Using alternation

There are three parts to this regular expression: the word boundaries on both ends, the noncapturing group, and the list of words (each separated by the ‹|› alternation operator). The word boundaries ensure that the regex does not match part of ...