Chapter 9 Regular Expressions

Ruby supports a built-in regular expressions feature. Regular expressions are strings that describe or match a set of other strings.

Regular expressions are written in the form of /pattern/modifiers. “Pattern” represents the regular expression itself while the “modifiers” refer to sets of characters indicating various options.

The following lists the components included in a regular expression:

• Literal Characters – Any literal character included in a regular expression matches itself in the string.

Example:

/c/

Ruby contains special characters such as ^, $, ?, ., /, \, [, ], {, }, (, ), +, and so forth. When you match one of these characters in a string, escape it with a backslash (\).

Example:

/\?/

* Wildcard character (.) – To match any character at some point in the pattern, use a special wildcard character. The wildcard character (.) matches any character with the exception of a newline.

Example:

/.ave/

The above regular expression matches “gave” or “save”. It even matches “%ave” or “2ave”.

• Character class – This refers to a list of characters which is placed inside a regular expression.

Example:

/[ gs] ave/

The above example shows that the regular expression matches either g or s, followed by ave. The expression only matches either “gave” or “save”.

A character class allows regular expressions to have multiple possible characters, but with a limited number of them.

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