Config::Properties - Read and write property files


  use Config::Properties;

  # reading...

  open my $fh, '<', 'my_config.props'
    or die "unable to open configuration file";

  my $properties = Config::Properties->new();

  $value = $properties->getProperty($key);

  # saving...

  open my $fh, '>', 'my_config.props'
    or die "unable to open configuration file for writing";

  $properties->setProperty($key, $value);

  $properties->format('%s => %s');
  $properties->store($fh, $header );


Config::Properties is a near implementation of the java.util.Properties API. It is designed to allow easy reading, writing and manipulation of Java-style property files.

The format of a Java-style property file is that of a key-value pair separated by either whitespace, the colon (:) character, or the equals (=) character. Whitespace before the key and on either side of the separator is ignored.

Lines that begin with either a hash (#) or a bang (!) are considered comment lines and ignored.

A backslash (\) at the end of a line signifies a continuation and the next line is counted as part of the current line (minus the backslash, any whitespace after the backslash, the line break, and any whitespace at the beginning of the next line).

The official references used to determine this format can be found in the Java API docs for java.util.Properties at

When a property file is saved it is in the format "key=value" for each line. This can be changed by setting the format attribute using either $object->format( $format_string ) or $object->setFormat( $format_string ) (they do the same thing). The format string is fed to printf and must contain exactly two %s format characters. The first will be replaced with the key of the property and the second with the value. The string can contain no other printf control characters, but can be anything else. A newline will be automatically added to the end of the string. The current format string can be obtained by using $object->format() (with no arguments) or $object->getFormat().

If a recent version of Text::Wrap is available, long lines are conveniently wrapped when saving.


Config::Property objects have this set of methods available:


Creates a new Config::Properties object.

The optional arguments are as follows:

file => $filename

Opens and reads the entries from the given properties file

format => $format

Sets the format using for saving the properties to a file. See "setFormat".

wrap => 0

Disables wrapping of long lines when saving the properties to a file.

defaults => $defaults

Default configuration values.

The given parameter can be a hash reference or another Config::Properties object.

In that way several configuration objects can be chained. For instance:

  my %defaults = (...);
  my $global_config = Config::Properties->new(file => '/etc/',
                                              defaults => \%defaults);
  my $user_config = Config::Properties->new(file => '/home/jsmith/.foo/',
                                            defaults => $global_config);
order => 'keep'|'alpha'|'none'

Sets how to order the properties when saved to a file or when returned by properties and propertyNames methods.

alpha sorts the keys in alphanumeric order. keep keeps the order of the properties as added or read from a file. none returns the properties unordered.

encoding => $encoding

IO encoding used to read the configuration file. See PerlIO.

When load is called the given encoding is used unless the file handler already has a encoding layer applied.

latin1 is used as the default encoding (as specified in the Java properties specification).

be_like_java => 1

When this feature is enabled, the module will try to mimic the Java implementation as much as possible when saving files.

Currently, some escaping rules are changed and line wrapping is disabled.


Calling new in this way is deprecated.

$p->getProperty($k, $default, $default2, ...)

return property $k or when not defined, the first defined $default*.

$p->requireProperty($k, $default, $default2, ...)

this method is similar to getProperty but dies if the requested property is not found.

$p->setProperty($k, $v)

set property $k value to $v.

$p->changeProperty($k, $v)
$p->changeProperty($k, $v, $default, $default2, ...)

method similar to setPropery but that does nothing when the new value is equal to the one returned by getProperty.

An example shows why it is useful:

  my $defaults=Config::Properties->new();
  $defaults->setProperty(foo => 'bar');

  my $p1=Config::Properties->new($defaults);
  $p1->setProperty(foo => 'bar');   # we set here!
  $p1->store(FILE1); foo gets saved on the file

  my $p2=Config::Properties->new($defaults);
  $p2->changeProperty(foo => 'bar'); # does nothing!
  $p2->store(FILE2); # foo doesn't get saved on the file
$p->deleteProperty($k, $recurse)

deletes property $k from the object.

If $recurse is true, it also deletes any $k property from the default properties object.


returns a flatten hash with all the property key/value pairs, i.e.:

  my %props=$p->properties;

returns a hash reference with all the properties (including those passed as defaults).


returns the names of all the properties (including those passed as defaults).

$p->splitToTree($regexp, $start)

builds a tree from the properties, splitting the keys with the regular expression $re (or /\./ by default). For instance:

  my $data = <<EOD;
  name = pete
  date.birth = 1958-09-12
  date.death = 2004-05-11
  surname = moo
  surname.length = 3

  open my $fh, '<', \$data;
  my $tree = $cfg->splitToTree();


  $tree = { date => { birth => '1958-09-12',
                      death => '2004-05-11' },
            name => 'pete',
            surname => { '' => 'moo',
                         length => '3' } };

The $start parameter allows to split only a subset of the properties. For instance, with the same data as on the previous example:

   my $subtree = $cfg->splitToTree(qr/\./, 'date');


  $tree = { birth => '1958-09-12',
            death => '2004-05-11' };
$p->setFromTree($tree, $separator)
$p->setFromTree($tree, $separator, $start)

This method sets properties from a tree of Perl hashes and arrays. It is the opposite of splitToTree.

$separator is the string used to join the parts of the property names. The default value is a dot (.).

$start is a string used as the starting point for the property names.

For instance:

  my $c = Config::Properties->new;
  $c->setFromTree( { foo => { '' => one,
                              hollo => [2, 3, 4, 1] },
                     bar => 'doo' },

  # sets properties:
  #      mama->bar = doo
  #      mama->foo = one
  #      mama->foo->hollo->0 = 2
  #      mama->foo->hollo->1 = 3
  #      mama->foo->hollo->2 = 4
  #      mama->foo->hollo->3 = 1
$p->changeFromTree($tree, $separator)
$p->changeFromTree($tree, $separator, $start)

similar to setFromTree but internally uses changeProperty instead of setProperty to set the property values.


loads properties from the open file $file.

Old properties on the object are discarded.

$p->save($file, $header)
$p->store($file, $header)

save the properties to the open file $file. Default properties are not saved.


similar to save, but instead of saving to a file, it returns a string with the content.


get/set the format string used when saving the object to a file.


Java docs for java.util.Properties at

Config::Properties::Simple for a simpler alternative interface to Config::Properties.


Add support for derived format as supported by Java class org.apache.commons.configuration.PropertiesConfiguration (


Config::Properties was originally developed by Randy Jay Yarger. It was maintained for some time by Craig Manley and finally it passed hands to Salvador Fandiño <>, the current maintainer.


Copyright 2001, 2002 by Randy Jay Yarger Copyright 2002, 2003 by Craig Manley. Copyright 2003-2009, 2011-2012, 2014-2015 by Salvador Fandiño.

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