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Janek Schleicher > File-Random > File::Random



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File::Random - Perl module for random selecting of a file


  use File::Random qw/:all/;
  my $fname  = random_file();

  my $fname2 = random_file(-dir => $dir);
  my $random_gif = random_file(
    -dir       => $dir,
    -check     => qr/\.gif$/,
        -recursive => 1,
    -follow => 1
  my $no_exe     = random_file(
    -dir   => $dir,
    -check => sub {! -x}
  my @jokes_of_the_day = content_of_random_file(-dir => '/usr/lib/jokes');
  my $joke_of_the_day  = content_of_random_file(-dir => '/usr/lib/jokes');
  # or the shorter
  my $joke = corf(-dir => '/usr/lib/jokes');
  my $word_of_the_day = random_line('/usr/share/dict/words');
  my @three_words     = random_line('/usr/share/dict/words',3);
  # or
  my ($title,$speech,$conclusion) = random_line('/usr/share/dict/words');


This module simplifies the routine job of selecting a random file. (As you can find at CGI scripts).

It's done, because it's boring (and errorprone), always to write something like

  my @files = (<*.*>);
  my $randf = $files[rand @files];


  opendir DIR, " ... " or die " ... ";
  my @files = grep {-f ...} (readdir DIR);
  closedir DIR;
  my $randf = $files[rand @files];

It also becomes very boring and very dangerous to write randomly selection for subdirectory searching with special check-routines.

The simple standard job of selecting a random line from a file is implemented, too.



Returns a randomly selected file(name) from the specified directory If the directory is empty, undef is returned. There are 3 options:

  my $file = random_file(
     -dir         => $dir, 
         -check       => qr/.../, # or sub { .... }
         -recursive   => 1        # or 0

Let's have a look to the options:

-dir (-d or -directory)

Specifies the directory where file has to come from.

If no -dir option is specified, a random file from the current directory will be used. That means '.' is the default for the -dir option.

-check (-c)

With the -check option you can either define a regex every filename has to follow, or a sub routine which gets the filename as argument. The filename passed as argument includes the relative path (relative to the -dir directory or the current directory). The argument is passed implicit as localized value of $_ and it is also the first parameter on the argument array $_[0].

Note, that -check doesn't accept anything else than a regexp or a subroutine. A string like '/.../' won't work.

The default is no checking (undef).

-recursive (-r or -rec)

Enables, that subdirectories are scanned for files, too. Every file, independent from its position in the file tree, has the same chance to be choosen. Now the relative path from the given subdirectory or the current directory of the randomly choosen file is included to the file name.

Every true value sets recursive behaviour on, every false value switches off. The default if false (undef).

Note, that I programmed the recursive routine very defendly (using File::Find). So switching -recursive on, slowers the program a bit :-) Please look to the File::Find module for any details and bugs related to recursive searching of files.

-follow (-f)

Follow symlinks when in recursive mode. See File::Find for details. Default is not to follow.

unknown options

Gives a warning. Unknown options are ignored. Note, that upper/lower case makes a difference.

FUNCTION content_of_random_file (or corf)

Returns the content of a randomly selected random file. In list context it returns an array of the lines of the selected file, in scalar context it returns a multiline string with whole the file. The lines aren't chomped.

This function has the same parameters and a similar behaviour to the random_file method. Note, that -check option still gets passed the filename and not the file content.

Instead of the long content_of_random_file, you can also use the alias corf (but don't forget to say either use File::Random qw/:all/ or use File::Random qw/corf/)

FUNCTION random_line($filename [, $nr_of_lines])

Returns one or $nr_of_lines random_lines from an (existing) file.

If the file is empty, undef is returned.

The algorithm used for returning one line is the one from the FAQ. See perldoc -q "random line" for details. For more than one line ($nr_of_lines > 1), I use nearly the same algorithm. Especially the returned lines aren't a sample, as a line could be returned doubled.

The result of random_line($filename, $nr) should be quite similar to map {random_line($filename)} (1 .. $nr), only the last way is not so efficient, as the file would be read $nr times instead of one times.

It also works on large files, as the algorithm only needs two lines of the file at the same time in memory.

$nr_of_lines is an optional argument which is 1 at default. Calling random_line in scalar context with $nr_of_lines greater than 1, gives a warning, as it doesn't make a lot of sense. I also gives you a warning of $nr_of_lines is zero.

You also can write something like

  my ($line1, $line2, $line3) = random_line($fname);

and random_line will return a list of 3 randomly choosen lines. Allthough File::Random tries its best to find out how many lines you wanted, it's not an oracle, so

  my @line = random_line($fname);

will be interpreted as

  my @line = random_line($fname,1);


None by default.

You can export the function random_file with use File::Random qw/random_file/;, use File::Random qw/content_of_random_file/ or with the more simple use File::Random qw/:all/;.

I didn't want to pollute namespaces as I could imagine, users write methods random_file to create a file with random content. If you think I'm paranoid, please tell me, then I'll take it into the export.


This module requires these other modules and libraries:


For the tests are also needed many more modules:


Test::Class itselfs needs the following additional modules: Attribute::Handlers Class::ISA IO::File Storable Test::Builder Test::Builder::Tester Test::Differences

All these modules are needed only for the tests. You can work with the module even without them. These modules are only needed for my test routines, not by the File::Random itself. (However, it's a good idea most to install most of the modules anyway).


A -firstline or -lines = [1 .. 10]> option for the content_of_random_file could be useful.

Also speed could be improved, as I tried to write the code very readable, but wasted sometimes a little bit speed.

Please feel free to suggest me anything what could be useful.


Well, because as this module handles some random data, it's a bit harder to test. So a test could be wrong, allthough everything is O.K.. To avoid it, I let many tests run, so that the chances for misproofing should be < 0.0000000001% or so. Even it has the disadvantage that the tests need really long :-(

I'm not definitly sure whether my test routines runs on OS, with path seperators different of '/', like in Win with '\\'. Perhaps anybody can try it and tell me the result. [But remember Win* is definitly the greater bug.]


This Program is free software. You can change or redistribute it under the same condition as Perl itself.

Copyright (c) 2002, Janek Schleicher, <>


Janek Schleicher, <>


Tie::Pick Data::Random Algorithm::Numerical::Sample

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