Regular Expressions Cookbook, 2nd Edition

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 complex examples of matching similar words are shown in Recipe 5.3.

Example JavaScript solution

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

// Solution 1:

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

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

// Solution 2 (reusable):

// 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 matchWords(subject, words) {
    var regexMetachars = /[(){[*+?.\\^$|]/g;

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

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

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

matchWords(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 ...