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version - Perl extension for Version Objects


  use version;
  $version = version->new("12.2.1"); # must be quoted for Perl < 5.8.1
  print $version;               # 12.2.1
  print $version->numify;       # 12.002001
  if ( $version gt  "12.2" )    # true

  $alphaver = version->new("1.2_3"); # must be quoted!
  print $alphaver;              # 1.2_3
  print $alphaver->is_alpha();  # true
  $ver = qv(1.2);               # 1.2.0
  $ver = qv("1.2");             # 1.2.0

  $perlver = version->new(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 in the appropriate context.

Both of these methods will produce similar version objects, in that the default stringification will yield the version "Normal Form" only if required:

  $v  = version->new(1.002);     # 1.002, but compares like 1.2.0
  $v  = version->new(1.002003);  # 1.2.3
  $v2 = version->new( "1.2.3");  # 1.2.3
  $v3 = version->new(  1.2.3);   # 1.2.3 for Perl >= 5.8.1

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 = version->new("99 and 94/100 percent pure"); # $v1 == 99.0
  $v2 = version->new("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. In both cases, a v-string encoded version will always be stringified in the version "Normal Form".

Consequently, the use of v-strings to initialize version objects with this module is only possible with Perl 5.8.1 or better (which 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, but only for purposes of comparison with other version objects. For example:

  $v = version->new(      1.2);    # prints 1.2, compares as 1.200.0
  $v = version->new(     1.02);    # prints 1.02, compares as 1.20.0
  $v = version->new(    1.002);    # prints 1.002, compares as 1.2.0
  $v = version->new(   1.0023);    # 1.2.300
  $v = version->new(  1.00203);    # 1.2.30
  $v = version->new( 1.002_03);    # 1.2.30   See "Quoting"
  $v = version->new( 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.

IMPORTANT NOTE: If your numeric version contains more than 3 significant digits after the decimal place, it will be split on each multiple of 3, so 1.0003 becomes 1.0.300, due to the need to remain compatible with Perl's own 5.005_03 == 5.5.30 interpretation.

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" (for all versions of Perl). If a Quoted Version has only one decimal place (and no embedded underscore), it is interpreted exactly like a "Numeric Version".

So, for example:

  $v = version->new( "1.002");    # 1.2
  $v = version->new( "1.2.3");    # 1.2.3
  $v = version->new("1.0003");    # 1.0.300

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:

      $VERSION = version->new(qw$Revision: 2.7 $);

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

      $VERSION = version->new("v2.7");

    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. The CVS $Revision$ increments differently from numeric versions (i.e. 1.10 follows 1.9), so it must be handled as if it were a "Quoted Version".

    New in 0.38, a new version object can be created as a copy of an existing version object:

      $v1 = version->new(12.3);
      $v2 = version->new($v1);

    and $v1 and $v2 will be identical.

  • qv()

    An alternate way to create a new version object is through the exported qv() sub. This is not strictly like other q? operators (like qq, qw), in that the only delimiters supported are parentheses (or spaces). It is the best way to initialize a short version without triggering the floating point interpretation. For example:

      $v1 = qv(1.2);         # 1.2.0
      $v2 = qv("1.2");       # also 1.2.0

    As you can see, either a bare number or a quoted string can be used, and either will yield the same version number.

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

  $ver   = version->new(""); # see "Quoting" below
  $alpha = version->new("1.2.3_4"); # see "Alpha versions" below
  $nver  = version->new(1.2);       # see "Numeric Versions" above
  • Normal Form

    For any version object which is initialized with multiple decimal places (either quoted or if possible v-string), or initialized using the qv() operator, the stringified representation is returned in a normalized or reduced form (no extraneous zeros):

      print $ver->normal;         # prints as 1.2.3
      print $ver->stringify;      # ditto
      print $ver;                 # ditto
      print $nver->normal;        # prints as 1.2.0
      print $nver->stringify;     # prints as 1.2, see "Stringification" 

    In order to preserve the meaning of the processed version, the normalized 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
  • 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
      print $nver->numify;        # prints 1.2

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

  • Stringification

    In order to mirror as much as possible the existing behavior of ordinary $VERSION scalars, the stringification operation will display differently, depending on whether the version was initialized as a "Numeric Version" or "Quoted Version".

    What this means in practice is that if the normal CPAN and Camel rules are followed ($VERSION is a floating point number with no more than 3 decimal places), the stringified output will be exactly the same as the numified output. There will be no visible difference, although the internal representation will be different, and the "Comparison operators" will function using the internal coding.

    If a version object is initialized using a "Quoted Version" form, or if the number of significant decimal places exceed three, then the stringified form will be the "Normal Form". The $obj->normal operation can always be used to produce the "Normal Form", even if the version was originally a "Numeric Version".

      print $ver->stringify;    # prints 1.2.3
      print $nver->stringify;   # prints 1.2
  • 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".

    WARNING: Comparing version with unequal numbers of decimal places (whether explicitely or implicitely initialized), may yield unexpected results at first glance. For example, the following inequalities hold:

      version->new(0.96)     > version->new(0.95); # 0.960.0 > 0.950.0
      version->new("0.96.1") < version->new(0.95); # 0.096.1 < 0.950.0

    For this reason, it is best to use either exclusively "Numeric Versions" or "Quoted Versions" with multiple decimal places.

  • Logical Operators

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

      $vobj = version->new($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 = version->new("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 one or more decimals 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:

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

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

  $version = version->new("v2.5.4");  # legal in all versions of Perl
  $newvers = version->new(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 the following:

      $VERSION = version->new(qw$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 = version->new("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.

    Alpha versions with a single decimal place will be treated exactly as if they were "Numeric Versions", for parsing purposes. The stringification for alpha versions with a single decimal place may seem suprising, since any trailing zeros will visible. For example, the above $alphaver will print as


    Alpha versions with more than a single decimal place will be treated exactly as if they were "Quoted Versions", and will display without any trailing (or leading) zeros, in the "Version Normal" form. For example,

      $newver = version->new("12.3.1_1");
      print $newver; # 12.3.1_1


In addition to the version objects, this modules also replaces the core UNIVERSAL::VERSION function with one that uses version objects for its comparisons. The return from this operator is always the numified form, and the warning message generated includes both the numified and normal forms (for clarity).

For example:

  package Foo;
  $VERSION = 1.2;

  package Bar;
  $VERSION = "1.3.5"; # works with all Perl's (since it is quoted)

  package main;
  use version;

  print $Foo::VERSION; # prints 1.2

  print $Bar::VERSION; # prints 1.003005

  eval "use CGI 10"; # some far future release
  print $@; # prints "CGI version 10 (10.0.0) required..."

IMPORTANT NOTE: This may mean that code which searches for a specific string (to determine whether a given module is available) may need to be changed.

The replacement UNIVERSAL::VERSION, when used as a function, like this:

  print $module->VERSION;

will follow the stringification rules; i.e. Numeric versions will be displayed with the numified format, and the rest will be displayed with the Normal format. Technically, the $module->VERSION function returns a string (PV) that can be converted to a number following the normal Perl rules, when used in a numeric context.


qv - quoted version initialization operator


John Peacock <jpeacock@rowman.com>



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