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John Peacock


version - Perl extension for Version Objects


  use version;
  $version = new version "12.2.1"; # must be quoted!
  print $version;               # 12.2.1
  print $version->numify;       # 12.002001
  if ( $version gt  "12.2" )    # true

  $vstring = new version qw(1.2); # must be quoted!
  print $vstring;               # 1.2

  $alphaver = new version "1.2_3"; # must be quoted!
  print $alphaver;              # 1.2_3
  print $alphaver->is_alpha();  # true

  $perlver = new version 5.005_03; # must not be quoted!
  print $perlver;               # 5.5.30


Overloaded version objects for all versions of Perl. This module implements all of the features of version objects which will be part of Perl 5.10.0 except automatic version object creation.

What IS a version

For the purposes of this module, a version "number" is a sequence of positive integral values separated by decimal points and optionally a single underscore. This corresponds to what Perl itself uses for a version, as well as extending the "version as number" that is discussed in the various editions of the Camel book.

There are actually two distinct ways to initialize versions:

  • Numeric Versions

    Any initial parameter which "looks like a number", see "Numeric Versions".

  • Quoted Versions

    Any initial parameter which contains more than one decimal point or contains an embedded underscore, see "Quoted Versions". The most recent development version of Perl (5.9.x) and the next major release (5.10.0) will automatically create version objects for bare numbers containing more than one decimal point.

Both of these methods will produce similar version objects, in that the default stringification will always be in a reduced form, i.e.:

  $v  = new version 1.002003;  # 1.2.3
  $v2 = new version  "1.2.3";  # 1.2.3
  $v3 = new version   1.2.3;   # 1.2.3 for Perl > 5.8.0

Note that the default stringification will display at least three sub terms (to ensure that appropriate round-trip processing is possible). Please see "Quoting" for more details on how Perl will parse various input values.

Any value passed to the new() operator will be parsed only so far as it contains a numeric, decimal, or underscore character. So, for example:

  $v1 = new version "99 and 94/100 percent pure"; # $v1 == 99.0
  $v2 = new version "something"; # $v2 == "" and $v2->numify == 0

However, see "New Operator" for one case where non-numeric text is acceptable when initializing version objects.

What about v-strings?

Beginning with Perl 5.6.0, an alternate method to code arbitrary strings of bytes was introduced, called v-strings. They were intended to be an easy way to enter, for example, Unicode strings (which contain two bytes per character). Some programs have used them to encode printer control characters (e.g. CRLF). They were also intended to be used for $VERSION. Their use has been problematic from the start and they will be phased out beginning in Perl 5.10.0.

There are two ways to enter v-strings: a bare number with two or more decimal places, or a bare number with one or more decimal places and a leading 'v' character (also bare). For example:

  $vs1 = 1.2.3; # encoded as \1\2\3
  $vs2 = v1.2;  # encoded as \1\2

The first of those two syntaxes is destined to be the default way to create a version object in 5.10.0, whereas the second will issue a mandatory deprecation warning beginning at the same time.

Consequently, the use of v-strings to initialize version objects with this module is only possible with Perl 5.8.1 (which will contain special code to enable it). Their use is strongly discouraged in all circumstances(especially the leading 'v' style), since the meaning will change depending on which Perl you are running. It is better to use "Quoted Versions" to ensure the proper interpretation.

Numeric Versions

These correspond to historical versions of Perl itself prior to 5.6.0, as well as all other modules which follow the Camel rules for the $VERSION scalar. A numeric version is initialized with what looks like a floating point number. Leading zeros are significant and trailing zeros are implied so that a minimum of three places is maintained between subversions. What this means is that any subversion (digits to the right of the decimal place) that contains less than three digits will have trailing zeros added to make up the difference. For example:

  $v = new version       1.2;    # 1.200
  $v = new version      1.02;    # 1.20
  $v = new version     1.002;    # 1.2
  $v = new version    1.0023;    # 1.2.300
  $v = new version   1.00203;    # 1.2.30
  $v = new version  1.002_03;    # 1.2.30   See "Quoting"
  $v = new version  1.002003;    # 1.2.3

All of the preceeding examples except the second to last are true whether or not the input value is quoted. The important feature is that the input value contains only a single decimal.

Quoted Versions

These are the newest form of versions, and correspond to Perl's own version style beginning with 5.6.0. Starting with Perl 5.10.0, and most likely Perl 6, this is likely to be the preferred form. This method requires that the input parameter be quoted, although Perl's after 5.9.0 can use bare numbers with multiple decimal places as a special form of quoting.

Unlike "Numeric Versions", Quoted Versions may have more than a single decimal point, e.g. "5.6.1" but must be quoted like this "5.6" in order to prevent the Numeric Version interpretation. Also unlike "Numeric Versions", leading zeros are not significant, and trailing zeros must be explicitely specified (i.e. will not be automatically added). In addition, the subversions are not enforced to be three decimal places.

So, for example:

  $v = new version   "1.002";    # 1.2
  $v = new version   "1.2.3";    # 1.2.3
  $v = new version   "1.2.3";    # 1.2.3
  $v = new version  "1.0003";    # 1.3

In addition to conventional versions, Quoted Versions can be used to create "Alpha Versions".

In general, Quoted Versions permit the greatest amount of freedom to specify a version, whereas Numeric Versions enforce a certain uniformity. See also "New Operator" for an additional method of initializing version objects.

Object Methods

Overloading has been used with version objects to provide a natural interface for their use. All mathematical operations are forbidden, since they don't make any sense for base version objects.

  • New Operator

    Like all OO interfaces, the new() operator is used to initialize version objects. One way to increment versions when programming is to use the CVS variable $Revision, which is automatically incremented by CVS every time the file is committed to the repository.

    In order to facilitate this feature, the following code can be employed:

      $VERSION = new version qw$Revision: 2.7 $;

    and the version object will be created as if the following code were used:

      $VERSION = new version "2.7";

    In other words, the version will be automatically parsed out of the string, and it will be quoted to preserve the meaning CVS normally carries for versions.

    For the subsequent examples, the following two objects will be used:

      $ver  = new version "1.2.3"; # see "Quoting" below
      $alpha = new version "1.2_3"; # see "Alpha versions" below
  • Stringification

    Any time a version object is used as a string, a stringified representation is returned in reduced form (no extraneous zeros):

      print $ver->stringify;      # prints 1.2.3
      print $ver;                 # same thing

    In order to preserve the meaning of the processed version, the default stringified representation will always contain at least three sub terms. In other words, the following is guaranteed to always be true:

      my $newver = version->new($ver->stringify);
      if ($newver eq $ver ) # always true

    If the string representation "looked like a number" then there is a possibility that creating a new version object from that would use the Numeric Version interpretation, If a version object contains only two terms internally, it will stringify with an explicit '.0' appended.

  • Numification

    Although all mathematical operations on version objects are forbidden by default, it is possible to retrieve a number which roughly corresponds to the version object through the use of the $obj->numify method. For formatting purposes, when displaying a number which corresponds a version object, all sub versions are assumed to have three decimal places. So for example:

      print $ver->numify;         # prints 1.002003

    Unlike the stringification operator, there is never any need to append trailing zeros to preserve the correct version value.

  • Comparison operators

    Both cmp and <=> operators perform the same comparison between terms (upgrading to a version object automatically). Perl automatically generates all of the other comparison operators based on those two. In addition to the obvious equalities listed below, appending a single trailing 0 term does not change the value of a version for comparison purposes. In other words "v1.2" and "1.2.0" will compare as identical.

    For example, the following relations hold:

      As Number       As String          Truth Value
      ---------       ------------       -----------
      $ver >  1.0     $ver gt "1.0"      true
      $ver <  2.5     $ver lt            true
      $ver != 1.3     $ver ne "1.3"      true
      $ver == 1.2     $ver eq "1.2"      false
      $ver == 1.2.3   $ver eq "1.2.3"    see discussion below

    It is probably best to chose either the numeric notation or the string notation and stick with it, to reduce confusion. Perl6 version objects may only support numeric comparisons. See also "Quoting".

  • Logical Operators

    If you need to test whether a version object has been initialized, you can simply test it directly:

      $vobj = new version $something;
      if ( $vobj )   # true only if $something was non-blank

    You can also test whether a version object is an "Alpha version", for example to prevent the use of some feature not present in the main release:

      $vobj = new version "1.2_3"; # MUST QUOTE
      if ( $vobj->is_alpha )       # True


Because of the nature of the Perl parsing and tokenizing routines, certain initialization values must be quoted in order to correctly parse as the intended version, and additionally, some initial values must not be quoted to obtain the intended version.

Except for "Alpha versions", any version initialized with something that looks like a number (a single decimal place) will be parsed in the same way whether or not the term is quoted. In order to be compatible with earlier Perl version styles, any use of versions of the form 5.006001 will be translated as 5.6.1. In other words, a version with a single decimal place will be parsed as implicitly having three places between subversions.

The complicating factor is that in bare numbers (i.e. unquoted), the underscore is a legal numeric character and is automatically stripped by the Perl tokenizer before the version code is called. However, if a number containing a single decimal and an underscore is quoted, i.e. not bare, that is considered a "Alpha Version" and the underscore is significant.

If you use a mathematic formula that resolves to a floating point number, you are dependent on Perl's conversion routines to yield the version you expect. You are pretty safe by dividing by a power of 10, for example, but other operations are not likely to be what you intend. For example:

  $VERSION = new version (qw$Revision: 1.4)[1]/10;
  print $VERSION;          # yields 0.14
  $V2 = new version 100/9; # Integer overflow in decimal number
  print $V2;               # yields 11_1285418553

Perl 5.8.1 and beyond will be able to automatically quote v-strings (although a warning will be issued under 5.9.x and 5.10.0), but that is not possible in earlier versions of Perl. In other words:

  $version = new version "v2.5.4";  # legal in all versions of Perl
  $newvers = new version v2.5.4;    # legal only in Perl > 5.8.1

Types of Versions Objects

There are two types of Version Objects:

  • Ordinary versions

    These are the versions that normal modules will use. Can contain as many subversions as required. In particular, those using RCS/CVS can use one of the following:

      $VERSION = new version qw$Revision: 2.7 $;

    and the current RCS Revision for that file will be inserted automatically. If the file has been moved to a branch, the Revision will have three or more elements; otherwise, it will have only two. This allows you to automatically increment your module version by using the Revision number from the primary file in a distribution, see "VERSION_FROM" in ExtUtils::MakeMaker.

  • Alpha versions

    For module authors using CPAN, the convention has been to note unstable releases with an underscore in the version string, see CPAN. Alpha releases will test as being newer than the more recent stable release, and less than the next stable release. For example:

      $alphaver = new version "12.3_1"; # must quote

    obeys the relationship

      12.3 < $alphaver < 12.4

    As a matter of fact, if is also true that

      12.3.0 < $alphaver < 12.3.1

    where the subversion is identical but the alpha release is less than the non-alpha release.


In addition to the version objects, this modules also replaces the core UNIVERSAL::VERSION function with one that uses version objects for its comparisons.


None by default.


John Peacock <jpeacock@rowman.com>



1 POD Error

The following errors were encountered while parsing the POD:

Around line 390:

You forgot a '=back' before '=head2'