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File::RandomLine - Retrieve random lines from a file


version 0.20


  # Fast but biased randomness
  use File::RandomLine;
  my $rl = File::RandomLine->new('/var/log/messages');
  print $rl->next;
  print join("\n",$rl->next(3));
  # Slow but uniform randomness
  $rl = File::RandomLine->new('/var/log/messages', {algorithm=>"uniform"});


This module provides a very fast random-access algorithm to retrieve random lines from a file. Lines are not retrieved with uniform probability, but instead are weighted by the number of characters in the previous line, due to the nature of the algorithm. Lines are most random when all lines are about the same length. For log file sampling or quote/fortune generation, this should be "random enough". Note -- when getting multiple lines, this module resamples with replacement, so duplicate lines are possible. Users will need to check for duplication on their own if this is not desired.

The algorithm is as follows:

  • Seek to a random location in the file

  • Read and discard the line fragment found

  • Read and return the next line, or the first line if we've reached the end of the file

  • Repeat until the requested number of random lines have been found

This module provides some similar behavior to File::Random, but the random access algorithm is much faster on large files. (E.g., it runs nearly instantaneously even on 100+ MB log files.)

This module also provides an optional, slower algorithm that returns random lines with uniform probability.



 $rl = File::RandomLine->new( "filename" );
 $rl = File::RandomLine->new( "filename", { algorithm => "uniform" } );

Returns a new File::RandomLine object for the given filename. The filename must refer to a readable file. A hash reference may be provided as an optional second argument to specify an algorithm to use. Currently supported algorithms are "fast" (the default) and "uniform". Under "uniform", the module indexes the entire file before selecting random lines with true uniform probability for each line. This can be significantly slower on large files.


 $line = $rl->next();
 @lines = $rl->next(5);
 ($line1, $line2, $line3) = $rl->next();

Returns one or more lines from the file. Without parameters, returns a single line if called in scalar context. With a positive integer parameter, returns a list with the specified number of lines. next also has some magic if called in list context with a finite length list of l-values and will return the proper number of lines.


Concept and code for "magic" behavior in array context taken from File::Random by Janek Schleicher.



Bugs / Feature Requests

Please report any bugs or feature requests through the issue tracker at You will be notified automatically of any progress on your issue.

Source Code

This is open source software. The code repository is available for public review and contribution under the terms of the license.

  git clone git://


David Golden <>


This software is Copyright (c) 2013 by David Golden.

This is free software, licensed under:

  The Apache License, Version 2.0, January 2004