by Ben Burkert


andexp makes it easy to generate random string from most regular expressions.


  • none!


$ sudo gem install randexp


Randexp adds the #generate (or #gen, for short) method to the Regexp class, which generates a 'random' string that will match your regular expression.

  # => "def"

Valid Regexp's

Randexp can only generate matching string from simple regular expression. Except for a few circumstances, wildcards are generally not allowed in the regular expression. is pretty domain specific, so trying to guess when to terminate a random pattern would produce unhelpful data:

>> /Aa{3}h*!/.gen
    # => RuntimeError: Sorry, "h*" is too vague, try setting a range: "h{0,3}"
>> /Aa{3}h{3,15}!/.gen
    => "Aaaahhhhh!"

>> /(never gonna (give you up|let you down), )*/.gen
    => RuntimeError: Sorry, "(...)*" is too vague, try setting a range: "(...){0, 3}"
>> /(never gonna (give you up|let you down), ){3,5}/.gen
    => "never gonna give you up, never gonna let you down, never gonna give you up, never gonna give you up, "

The exception being word characters (w), which generate a random word from the Dictionary class.

>> /\w+/.gen
    => "groveling"

Primitives & Complex matches

The single character matchers supported are words(w), whitespace(s), and digits(d).

>> /\d{50}/.gen
    => "50315410741096763188525493528315906035878741451037"

When a multiplicity constraint is placed on a word character, a word with the valid length is generated.

>> /\w{10}/.gen  # a word with 10 letters
    => "Chaucerism"

>> /\w{5,15}/.gen
    => "cabalistic"

Complex matchers use the [:…:] syntax within the regular expression.

>> /[:sentence:]/.gen
    => "Nonhearer demetricize toppiece filicic possessedness rhodizite zoomagnetism earwigginess steady"

Complex matchers can also be added by extending the Randgen class.

class Randgen
  def self.serial_number(options = {})

>> /[:serial_number:]/.gen
    => "XX3770-M-33114"


The Dictionary loads the local users' words file, allowing randomly generated words to be chosen from thousands of entries to the words file. Words are mapped by their length to allow words to be randomly chosen based on size.