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String::Random - Perl module to generate random strings based on a pattern


version 0.32


    use String::Random;
    my $string_gen = String::Random->new;
    print $string_gen->randregex('\d\d\d'); # Prints 3 random digits
    # Prints 3 random printable characters
    print $string_gen->randpattern("...");


    use String::Random qw(random_regex random_string);
    print random_regex('\d\d\d'); # Also prints 3 random digits
    print random_string("...");   # Also prints 3 random printable characters


This module makes it trivial to generate random strings.

As an example, let's say you are writing a script that needs to generate a random password for a user. The relevant code might look something like this:

    use String::Random;
    my $pass = String::Random->new;
    print "Your password is ", $pass->randpattern("CCcc!ccn"), "\n";

This would output something like this:

  Your password is UDwp$tj5

NOTE!!!: currently, String::Random defaults to Perl's built-in predictable random number generator so the passwords generated by it are insecure. See the rand_gen option to String::Random constructor to specify a more secure random number generator. There is no equivalent to this in the procedural interface, you must use the object-oriented interface to get this functionality.

If you are more comfortable dealing with regular expressions, the following code would have a similar result:

  use String::Random;
  my $pass = String::Random->new;
  print "Your password is ",
      $pass->randregex('[A-Z]{2}[a-z]{2}.[a-z]{2}\d'), "\n";


The pre-defined patterns (for use with randpattern() and random_pattern()) are as follows:

  c        Any Latin lowercase character [a-z]
  C        Any Latin uppercase character [A-Z]
  n        Any digit [0-9]
  !        A punctuation character [~`!@$%^&*()-_+={}[]|\:;"'.<>?/#,]
  .        Any of the above
  s        A "salt" character [A-Za-z0-9./]
  b        Any binary data

These can be modified, but if you need a different pattern it is better to create another pattern, possibly using one of the pre-defined as a base. For example, if you wanted a pattern A that contained all upper and lower case letters ([A-Za-z]), the following would work:

  my $gen = String::Random->new;
  $gen->{'A'} = [ 'A'..'Z', 'a'..'z' ];


  my $gen = String::Random->new;
  $gen->{'A'} = [ @{$gen->{'C'}}, @{$gen->{'c'}} ];


  my $gen = String::Random->new;
  $gen->set_pattern(A => [ 'A'..'Z', 'a'..'z' ]);

The random_string function, described below, has an alternative interface for adding patterns.


new max => number
new rand_gen => sub

Create a new String::Random object.

Optionally a parameter max can be included to specify the maximum number of characters to return for * and other regular expression patterns that do not return a fixed number of characters.

Optionally a parameter rand_gen can be included to specify a subroutine coderef for generating the random numbers used in this module. The coderef must accept one argument max and return an integer between 0 and max - 1. The default rand_gen coderef is

 sub {
     my ($max) = @_;
     return int rand $max;
randpattern LIST

The randpattern method returns a random string based on the concatenation of all the pattern strings in the list.

It will return a list of random strings corresponding to the pattern strings when used in list context.

randregex LIST

The randregex method returns a random string that will match the regular expression passed in the list argument.

Please note that the arguments to randregex are not real regular expressions. Only a small subset of regular expression syntax is actually supported. So far, the following regular expression elements are supported:

  \w    Alphanumeric + "_".
  \d    Digits.
  \W    Printable characters other than those in \w.
  \D    Printable characters other than those in \d.
  .     Printable characters.
  []    Character classes.
  {}    Repetition.
  *     Same as {0,}.
  ?     Same as {0,1}.
  +     Same as {1,}.

Regular expression support is still somewhat incomplete. Currently special characters inside [] are not supported (with the exception of "-" to denote ranges of characters). The parser doesn't care for spaces in the "regular expression" either.

get_pattern STRING

Return a pattern given a name.

  my $gen = String::Random->new;

(Added in version 0.32.)


Add or redefine a pattern given a name and a character set.

  my $gen = String::Random->new;
  $gen->set_pattern(A => [ 'A'..'Z', 'a'..'z' ]);

(Added in version 0.32.)


IGNORE! - for compatibility with an old version. DO NOT USE!


random_string PATTERN,LIST
random_string PATTERN

When called with a single scalar argument, random_string returns a random string using that scalar as a pattern. Optionally, references to lists containing other patterns can be passed to the function. Those lists will be used for 0 through 9 in the pattern (meaning the maximum number of lists that can be passed is 10). For example, the following code:

    print random_string("0101",
                        ["a", "b", "c"],
                        ["d", "e", "f"]), "\n";

would print something like this:

random_regex REGEX_IN_STRING

Prints a string for the regular expression given as the string. See the synposis for example.


This is Bug Free™ code. (At least until somebody finds one…)

Please report bugs here: .


Original Author: Steven Pritchard

Now maintained by: Shlomi Fish ( ).


This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.





The following websites have more information about this module, and may be of help to you. As always, in addition to those websites please use your favorite search engine to discover more resources.

Bugs / Feature Requests

Please report any bugs or feature requests by email to bug-string-random at, or through the web interface at You will be automatically notified of any progress on the request by the system.

Source Code

The code is open to the world, and available for you to hack on. Please feel free to browse it and play with it, or whatever. If you want to contribute patches, please send me a diff or prod me to pull from your repository :)

  git clone


Shlomi Fish <>


Please report any bugs or feature requests on the bugtracker website

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.


This software is copyright (c) 2021 by Shlomi Fish.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.