Regular expressions

A regular expression is a succinct way of describing strings, typically used in searching for a pattern, subject to modifiers that indicate when the pattern should apply. The syntax used is /pattern/modifiers.

Modifiers

The following modifiers can be used, singly or in combination.

For example, /a/g can be used to find lower-case a's, and /a/gi can be used to find lower-case a's and upper-case A's. Similarly, a string can be used instead of a single character, such as /out/g being used to find all matches with the string "out".

Methods using regular expressions

The string method .search(exp) consumes a regular expression and produces the position of the first match, and the string method .replace(exp, replace) consumes a regular expression and replacement string and produces the string formed by replacing each substring matching the pattern by the replacement string.

For a string stored in the variable example:

• example.search(/a/) finds the position of the first lower-case a
• example.replace(/a/g/, "?") replaces each lower-case a with a question mark
• example.search(/a/i) find the position of the first a, lower-case or upper-case
• example.replace(/the/gi, "?") replaces the string the with a question mark, whether the letters are lower-case or upper-case