Ruby Tutorial: Regexp

Regular Expressions

Regular expressions are terribly powerful, and terribly complicated. They could easily fill a two-day (or longer) class on their own. In this section we will assume you know something about them already, and just cover the basic syntax and point you to some deeper references.

Ref. WGR Chapter 11, Regular expressions and regexp-based string operations

regex literals

@@@ ruby
word_exp = /\b[a-z]*\b/i
  • slashes delineate the pattern
  • backslash b means "match a word boundary"
  • brackets delineate a match of a single character (aka "character class")
  • a hyphen z means "all the letters between a and z, inclusive"
  • star means match any number (0 or more) of the previous character (or, as in this case, character class)
  • slash i at the end means "ignore capitalization" (or "case insensitive")

So the above expression will match any word containing only normal English letters, in any combination of upper- or lowercase.

regex operators

equal tilde returns the position in the string that matches, or nil if no match

@@@ ruby
>> "abcde" =~ /bcd/
=> 1

bang tilde returns false if the string matches, or true if it doesn't

@@@ ruby
>> "abcde" !~ /xyz/
=> true
>> "abcde" !~ /bcd/
=> false

operations that use regexes

String#split

Array#grep

String#gsub

learning more

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