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generate random data from a Regular Expression
Branch: master



by Ben Burkert


randexp 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.

>> /abc|def/.gen

  1. => “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.

Real Names

One can easily generate real names based on a wordlist.

Random first name (male or female):

>> Randgen.first_name => "Malika"

Random first name, with a specific gender:

>> Randgen.first_name(:gender => :male) => "Rick"

Random first name, with a specific gender & length:

>> Randgen.first_name(:gender => :male, :length => 10) => "Kristopher"

Random last name:

>> Randgen.last_name => "Klocko"

Random name:

>> => "Rosendo Raynor"


>> /[:name:]/.gen => "Marc Adams"

Random name, with a specific gender:

>> => :female) => "Tatiana Brakus"


  • Matt Aimonetti (mattetti)
  • Gerrit Kaiser (gerrit)
  • Mike Vincent (shame)
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