Ruby Regular Expression

A regular expression is also spelled as regexp which holds a regular expression, used to match a pattern against strings. In Ruby, a pattern is written between forward slash characters. They describe the content of a string. Ruby regular expression is more similar to Perl regular expression.

Syntax:

/search string/  

Ruby 1.9 uses Oniguruma regular expressions library but Ruby 2.0 uses Onigmo regular expressions library. Onigmo is a fork library of Oniguruma adding some new features.

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=∽ and #match operators

The pattern matching is achieved by using =∽ and #match operators.Backward Skip 10sPlay VideoForward Skip 10s

=∽

This is the basic matching pattern. Here two operands are used. One is a regular expression and other is a string. The regular expression is matched with the string.

If a match is found, the operator returns index of first match otherwise nil.

Example:

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#match

This operator returns a MatchData object on matching otherwise nil.

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Metacharacters and Escapes

Metacharacters have specific meaning in a pattern. To match a string, they are back slashed (\\\) or escaped. Some meta characters are (,), (.), (?), (+), (-), (*), [,], {,}.

It returns the specific string when matched otherwise nil.

Example:

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Characters Classes

Metacharacters have specific meaning in a pattern. To match a string, they are back slashed (\\\) or escaped.

A character class is encircled within square brackets.

[ab]

Here, [ab] means a or b. It is the oppoite of /ab/ which means a and b.

Example:

[a-d]

Here, [a-d] is equivalent to [abcd]. The hyphen (-) character class represents range of characters.

[^a-d]

The ^ sign represents any other character which is not present in the range.

Example: