How do I match an entire string with a regex?

Solution 1:

Try the following regular expression:

^Red October$

By default, regular expressions are case sensitive. The ^ marks the start of the matching text and $ the end.

Solution 2:

Generally, and with default settings, ^ and $ anchors are a good way of ensuring that a regex matches an entire string.

A few caveats, though:

If you have alternation in your regex, be sure to enclose your regex in a non-capturing group before surrounding it with ^ and $:

^foo|bar$

is of course different from

^(?:foo|bar)$

Also, ^ and $ can take on a different meaning (start/end of line instead of start/end of string) if certain options are set. In text editors that support regular expressions, this is usually the default behaviour. In some languages, especially Ruby, this behaviour cannot even be switched off.

Therefore there is another set of anchors that are guaranteed to only match at the start/end of the entire string:

\A matches at the start of the string.

\Z matches at the end of the string or before a final line break.

\z matches at the very end of the string.

But not all languages support these anchors, most notably JavaScript.

Solution 3:

Use the ^ and $ modifiers to denote where the regex pattern sits relative to the start and end of the string:

Regex.Match("Red October", "^Red October$"); // pass
Regex.Match("The Hunt for Red October", "^Red October$"); // fail