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Manual Reference Pages  - Dpkg::Deps (3)


Dpkg::Deps - parse and manipulate dependencies of Debian packages



The Dpkg::Deps module provides objects implementing various types of dependencies.

The most important function is deps_parse(), it turns a dependency line in a set of Dpkg::Deps::{Simple,AND,OR,Union} objects depending on the case.


All the deps_* functions are exported by default.
deps_eval_implication($rel_p, $v_p, $rel_q, $v_q) ($rel_p, $v_p) and ($rel_q, $v_q) express two dependencies as (relation, version). The relation variable can have the following values that are exported by Dpkg::Version: REL_EQ, REL_LT, REL_LE, REL_GT, REL_GT.

This functions returns 1 if the p dependency implies the q dependency. It returns 0 if the p dependency implies that q is not satisfied. It returns undef when there’s no implication.

The $v_p and $v_q parameter should be Dpkg::Version objects.

my $dep = deps_parse($line, %options) This function parses the dependency line and returns an object, either a Dpkg::Deps::AND or a Dpkg::Deps::Union. Various options can alter the behaviour of that function.
use_arch (defaults to 1) Take into account the architecture restriction part of the dependencies. Set to 0 to completely ignore that information.
host_arch (defaults to the current architecture) Define the host architecture. By default it uses Dpkg::Arch::get_host_arch() to identify the proper architecture.
reduce_arch (defaults to 0) If set to 1, ignore dependencies that do not concern the current host architecture. This implicitely strips off the architecture restriction list so that the resulting dependencies are directly applicable to the current architecture.
union (defaults to 0) If set to 1, returns a Dpkg::Deps::Union instead of a Dpkg::Deps::AND. Use this when parsing non-dependency fields like Conflicts.
build_dep (defaults to 0) If set to 1, allow build-dep only arch qualifiers, that is “:native”. This should be set whenever working with build-deps.
deps_compare($a, $b) Implements a comparison operator between two dependency objects. This function is mainly used to implement the sort() method.

OBJECTS - Dpkg::Deps::*

There are several kind of dependencies. A Dpkg::Deps::Simple dependency represents a single dependency statement (it relates to one package only). Dpkg::Deps::Multiple dependencies are built on top of this object and combine several dependencies in a different manners. Dpkg::Deps::AND represents the logical AND between dependencies while Dpkg::Deps::OR represents the logical OR. Dpkg::Deps::Multiple objects can contain Dpkg::Deps::Simple object as well as other Dpkg::Deps::Multiple objects.

In practice, the code is only meant to handle the realistic cases which, given Debian’s dependencies structure, imply those restrictions: AND can contain Simple or OR objects, OR can only contain Simple objects.

Dpkg::Deps::KnownFacts is a special object that is used while evaluating dependencies and while trying to simplify them. It represents a set of installed packages along with the virtual packages that they might provide.

    Common functions

$dep->is_empty() Returns true if the dependency is empty and doesn’t contain any useful information. This is true when a Dpkg::Deps::Simple object has not yet been initialized or when a (descendant of) Dpkg::Deps::Multiple contains an empty list of dependencies.
$dep->get_deps() Returns a list of sub-dependencies. For Dpkg::Deps::Simple it returns itself.
‘‘$dep’’ Returns a string representing the dependency. If $fh is set, it prints the string to the filehandle.
$dep->implies($other_dep) Returns 1 when $dep implies $other_dep. Returns 0 when $dep implies NOT($other_dep). Returns undef when there’s no implication. $dep and $other_dep do not need to be of the same type.
$dep->sort() Sorts alphabetically the internal list of dependencies. It’s a no-op for Dpkg::Deps::Simple objects.
$dep->arch_is_concerned($arch) Returns true if the dependency applies to the indicated architecture. For multiple dependencies, it returns true if at least one of the sub-dependencies apply to this architecture.
$dep->reduce_arch($arch) Simplifies the dependency to contain only information relevant to the given architecture. A Dpkg::Deps::Simple object can be left empty after this operation. For Dpkg::Deps::Multiple objects, the non-relevant sub-dependencies are simply removed.

This trims off the architecture restriction list of Dpkg::Deps::Simple objects.

$dep->get_evaluation($facts) Evaluates the dependency given a list of installed packages and a list of virtual packages provided. Those lists are part of the Dpkg::Deps::KnownFacts object given as parameters.

Returns 1 when it’s true, 0 when it’s false, undef when some information is lacking to conclude.

$dep->simplify_deps($facts, @assumed_deps) Simplifies the dependency as much as possible given the list of facts (see object Dpkg::Deps::KnownFacts) and a list of other dependencies that are known to be true.
$dep->has_arch_restriction() For a simple dependency, returns the package name if the dependency applies only to a subset of architectures. For multiple dependencies, it returns the list of package names that have such a restriction.
$dep->reset() Clears any dependency information stored in $dep so that $dep->is_empty() returns true.


Such an object has four interesting properties:
package The package name (can be undef if the dependency has not been initialized or if the simplification of the dependency lead to its removal).
relation The relational operator: =, <<, <=, >= or >>. It can be undefined if the dependency had no version restriction. In that case the following field is also undefined.
version The version.
arches The list of architectures where this dependency is applicable. It’s undefined when there’s no restriction, otherwise it’s an array ref. It can contain an exclusion list, in that case each architecture is prefixed with an exclamation mark.
archqual The arch qualifier of the dependency (can be undef if there’s none). In the dependency python:any (>= 2.6), the arch qualifier is any.
$simple_dep->parse_string(‘‘dpkg-dev (>= 1.14.8) [!hurd-i386]’’) Parses the dependency and modifies internal properties to match the parsed dependency.
$simple_dep->merge_union($other_dep) Returns true if $simple_dep could be modified to represent the union of both dependencies. Otherwise returns false.


This is the base class for Dpkg::Deps::{AND,OR,Union}. It implements the following methods:
$mul->add($dep) Adds a new dependency object at the end of the list.


This object represents a list of dependencies who must be met at the same time.
$and->output([$fh]) The output method uses , to join the list of sub-dependencies.


This object represents a list of dependencies of which only one must be met for the dependency to be true.
$or->output([$fh]) The output method uses | to join the list of sub-dependencies.


This object represents a list of relationships.
$union->output([$fh]) The output method uses , to join the list of relationships.
$union->get_evaluation($other_dep) Those methods are not meaningful for this object and always return undef.
$union->simplify_deps($facts) The simplication is done to generate an union of all the relationships. It uses $simple_dep->merge_union($other_dep) to get its job done.


This object represents a list of installed packages and a list of virtual packages provided (by the set of installed packages).
my $facts = Dpkg::Deps::KnownFacts->new(); Creates a new object.
$facts->add_installed_package($package, $version, $arch, $multiarch) Records that the given version of the package is installed. If $version/$arch is undefined we know that the package is installed but we don’t know which version/architecture it is. $multiarch is the Multi-Arch field of the package. If $multiarch is undef, it will be equivalent to Multi-Arch: no.

Note that $multiarch is only used if $arch is provided.

$facts->add_provided_package($virtual, $relation, $version, $by) Records that the $by package provides the $virtual package. $relation and $version correspond to the associated relation given in the Provides field. This might be used in the future for versioned provides.
my ($check, $param) = $facts->check_package($package) $check is one when the package is found. For a real package, $param contains the version. For a virtual package, $param contains an array reference containing the list of packages that provide it (each package is listed as [ $provider, $relation, $version ]).

This function is obsolete and should not be used. Dpkg::Deps::KnownFacts is only meant to be filled with data and then passed to Dpkg::Deps methods where appropriate, but it should not be directly queried.


    Version 1.01

o Add new $dep->reset() method that all dependency objects support.
o Dpkg::Deps::Simple now recognizes the arch qualifier any and stores it in the archqual property when present.
o Dpkg::Deps::KnownFacts->add_installed_package() now accepts 2 supplementary parameters ($arch and $multiarch).
o Dpkg::Deps::KnownFacts->check_package() is obsolete, it should not have been part of the public API.

1.16.12 Dpkg::Deps (3) 2013-09-30
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