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method

new

v2_6_3 - Show latest stable - Class: Regexp
new(*args)
public

Constructs a new regular expression from pattern, which can be either a String or a Regexp (in which case that regexp’s options are propagated), and new options may not be specified (a change as of Ruby 1.8).

If options is an Integer, it should be one or more of the constants Regexp::EXTENDED, Regexp::IGNORECASE, and Regexp::MULTILINE, or-ed together. Otherwise, if options is not nil or false, the regexp will be case insensitive.

r1 = Regexp.new('^a-z+:\\s+\w+') #=> /^a-z+:\s+\w+/
r2 = Regexp.new('cat', true)     #=> /cat/i
r3 = Regexp.new(r2)              #=> /cat/i
r4 = Regexp.new('dog', Regexp::EXTENDED | Regexp::IGNORECASE) #=> /dog/ix

2Notes

Multiline regexps

mutru · Feb 4, 20093 thanks

A shortcut for multiline regular expressions is

/First line.*Other line/m

(notice the trailing /m)

For example:

text = <<-END
Hello world!
This is a test.
END

text.match(/world.*test/m).nil?  #=> false
text.match(/world.*test/).nil?   #=> true

Other regular-expression modifiers

Soleone · Feb 11, 20093 thanks

Likewise you can set Regexp::IGNORECASE directly on the regexp with the literal syntax:

/first/i
# This will match "first", "First" and even "fiRSt"

Even more modifiers

  • o -- Perform #{} interpolations only once, the first time the regexp literal is evaluated.

  • x -- Ignores whitespace and allows comments in * regular expressions

  • u, e, s, n -- Interpret the regexp as Unicode (UTF-8), EUC, SJIS, or ASCII. If none of these modifiers is specified, the regular expression is assumed to use the source encoding.

=== Literal to the rescue Like string literals delimited with %Q, Ruby allows you to begin your regular expressions with %r followed by a delimiter of your choice.

This is useful when the pattern you are describing contains a lot of forward slash characters that you don't want to escape:

%Q(http://)
# This will match "http://"