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CPAN.pm

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README
NAME
    CPAN - query, download and build perl modules from CPAN sites

SYNOPSIS
    Interactive mode:

      perl -MCPAN -e shell

    --or--

      cpan

    Basic commands:

      # Modules:

      cpan> install Acme::Meta                       # in the shell

      CPAN::Shell->install("Acme::Meta");            # in perl

      # Distributions:

      cpan> install NWCLARK/Acme-Meta-0.02.tar.gz    # in the shell

      CPAN::Shell->
        install("NWCLARK/Acme-Meta-0.02.tar.gz");    # in perl

      # module objects:

      $mo = CPAN::Shell->expandany($mod);
      $mo = CPAN::Shell->expand("Module",$mod);      # same thing

      # distribution objects:

      $do = CPAN::Shell->expand("Module",$mod)->distribution;
      $do = CPAN::Shell->expandany($distro);         # same thing
      $do = CPAN::Shell->expand("Distribution",
                                $distro);            # same thing

DESCRIPTION
    The CPAN module automates or at least simplifies the make and install of
    perl modules and extensions. It includes some primitive searching
    capabilities and knows how to use Net::FTP or LWP or some external
    download clients to fetch the distributions from the net.

    These are fetched from one or more of the mirrored CPAN (Comprehensive
    Perl Archive Network) sites and unpacked in a dedicated directory.

    The CPAN module also supports the concept of named and versioned
    *bundles* of modules. Bundles simplify the handling of sets of related
    modules. See Bundles below.

    The package contains a session manager and a cache manager. The session
    manager keeps track of what has been fetched, built and installed in the
    current session. The cache manager keeps track of the disk space
    occupied by the make processes and deletes excess space according to a
    simple FIFO mechanism.

    All methods provided are accessible in a programmer style and in an
    interactive shell style.

  CPAN::shell([$prompt, $command]) Starting Interactive Mode
    The interactive mode is entered by running

        perl -MCPAN -e shell

    or

        cpan

    which puts you into a readline interface. If "Term::ReadKey" and either
    "Term::ReadLine::Perl" or "Term::ReadLine::Gnu" are installed it
    supports both history and command completion.

    Once you are on the command line, type "h" to get a one page help screen
    and the rest should be self-explanatory.

    The function call "shell" takes two optional arguments, one is the
    prompt, the second is the default initial command line (the latter only
    works if a real ReadLine interface module is installed).

    The most common uses of the interactive modes are

    Searching for authors, bundles, distribution files and modules
      There are corresponding one-letter commands "a", "b", "d", and "m" for
      each of the four categories and another, "i" for any of the mentioned
      four. Each of the four entities is implemented as a class with
      slightly differing methods for displaying an object.

      Arguments you pass to these commands are either strings exactly
      matching the identification string of an object or regular expressions
      that are then matched case-insensitively against various attributes of
      the objects. The parser recognizes a regular expression only if you
      enclose it between two slashes.

      The principle is that the number of found objects influences how an
      item is displayed. If the search finds one item, the result is
      displayed with the rather verbose method "as_string", but if we find
      more than one, we display each object with the terse method
      "as_glimpse".

    "get", "make", "test", "install", "clean" modules or distributions
      These commands take any number of arguments and investigate what is
      necessary to perform the action. If the argument is a distribution
      file name (recognized by embedded slashes), it is processed. If it is
      a module, CPAN determines the distribution file in which this module
      is included and processes that, following any dependencies named in
      the module's META.yml or Makefile.PL (this behavior is controlled by
      the configuration parameter "prerequisites_policy".)

      "get" downloads a distribution file and untars or unzips it, "make"
      builds it, "test" runs the test suite, and "install" installs it.

      Any "make" or "test" are run unconditionally. An

        install <distribution_file>

      also is run unconditionally. But for

        install <module>

      CPAN checks if an install is actually needed for it and prints *module
      up to date* in the case that the distribution file containing the
      module doesn't need to be updated.

      CPAN also keeps track of what it has done within the current session
      and doesn't try to build a package a second time regardless if it
      succeeded or not. It does not repeat a test run if the test has been
      run successfully before. Same for install runs.

      The "force" pragma may precede another command (currently: "get",
      "make", "test", or "install") and executes the command from scratch
      and tries to continue in case of some errors. See the section below on
      the "force" and the "fforce" pragma.

      The "notest" pragma may be used to skip the test part in the build
      process.

      Example:

          cpan> notest install Tk

      A "clean" command results in a

        make clean

      being executed within the distribution file's working directory.

    "readme", "perldoc", "look" module or distribution
      "readme" displays the README file of the associated distribution.
      "Look" gets and untars (if not yet done) the distribution file,
      changes to the appropriate directory and opens a subshell process in
      that directory. "perldoc" displays the pod documentation of the module
      in html or plain text format.

    "ls" author
    "ls" globbing_expression
      The first form lists all distribution files in and below an author's
      CPAN directory as they are stored in the CHECKUMS files distributed on
      CPAN. The listing goes recursive into all subdirectories.

      The second form allows to limit or expand the output with shell
      globbing as in the following examples:

            ls JV/make*
            ls GSAR/*make*
            ls */*make*

      The last example is very slow and outputs extra progress indicators
      that break the alignment of the result.

      Note that globbing only lists directories explicitly asked for, for
      example FOO/* will not list FOO/bar/Acme-Sthg-n.nn.tar.gz. This may be
      regarded as a bug and may be changed in future versions.

    "failed"
      The "failed" command reports all distributions that failed on one of
      "make", "test" or "install" for some reason in the currently running
      shell session.

    Persistence between sessions
      If the "YAML" or the "YAML::Syck" module is installed a record of the
      internal state of all modules is written to disk after each step. The
      files contain a signature of the currently running perl version for
      later perusal.

      If the configurations variable "build_dir_reuse" is set to a true
      value, then CPAN.pm reads the collected YAML files. If the stored
      signature matches the currently running perl the stored state is
      loaded into memory such that effectively persistence between sessions
      is established.

    The "force" and the "fforce" pragma
      To speed things up in complex installation scenarios, CPAN.pm keeps
      track of what it has already done and refuses to do some things a
      second time. A "get", a "make", and an "install" are not repeated. A
      "test" is only repeated if the previous test was unsuccessful. The
      diagnostic message when CPAN.pm refuses to do something a second time
      is one of *Has already been *"unwrapped|made|tested successfully" or
      something similar. Another situation where CPAN refuses to act is an
      "install" if the according "test" was not successful.

      In all these cases, the user can override the goatish behaviour by
      prepending the command with the word force, for example:

        cpan> force get Foo
        cpan> force make AUTHOR/Bar-3.14.tar.gz
        cpan> force test Baz
        cpan> force install Acme::Meta

      Each *forced* command is executed with the according part of its
      memory erased.

      The "fforce" pragma is a variant that emulates a "force get" which
      erases the entire memory followed by the action specified, effectively
      restarting the whole get/make/test/install procedure from scratch.

    Lockfile
      Interactive sessions maintain a lockfile, per default "~/.cpan/.lock".
      Batch jobs can run without a lockfile and do not disturb each other.

      The shell offers to run in *degraded mode* when another process is
      holding the lockfile. This is an experimental feature that is not yet
      tested very well. This second shell then does not write the history
      file, does not use the metadata file and has a different prompt.

    Signals
      CPAN.pm installs signal handlers for SIGINT and SIGTERM. While you are
      in the cpan-shell it is intended that you can press "^C" anytime and
      return to the cpan-shell prompt. A SIGTERM will cause the cpan-shell
      to clean up and leave the shell loop. You can emulate the effect of a
      SIGTERM by sending two consecutive SIGINTs, which usually means by
      pressing "^C" twice.

      CPAN.pm ignores a SIGPIPE. If the user sets "inactivity_timeout", a
      SIGALRM is used during the run of the "perl Makefile.PL" or "perl
      Build.PL" subprocess.

  CPAN::Shell
    The commands that are available in the shell interface are methods in
    the package CPAN::Shell. If you enter the shell command, all your input
    is split by the Text::ParseWords::shellwords() routine which acts like
    most shells do. The first word is being interpreted as the method to be
    called and the rest of the words are treated as arguments to this
    method. Continuation lines are supported if a line ends with a literal
    backslash.

  autobundle
    "autobundle" writes a bundle file into the
    "$CPAN::Config->{cpan_home}/Bundle" directory. The file contains a list
    of all modules that are both available from CPAN and currently installed
    within @INC. The name of the bundle file is based on the current date
    and a counter.

  hosts
    Note: this feature is still in alpha state and may change in future
    versions of CPAN.pm

    This commands provides a statistical overview over recent download
    activities. The data for this is collected in the YAML file
    "FTPstats.yml" in your "cpan_home" directory. If no YAML module is
    configured or YAML not installed, then no stats are provided.

  mkmyconfig
    mkmyconfig() writes your own CPAN::MyConfig file into your ~/.cpan/
    directory so that you can save your own preferences instead of the
    system wide ones.

  recent ***EXPERIMENTAL COMMAND***
    The "recent" command downloads a list of recent uploads to CPAN and
    displays them *slowly*. While the command is running $SIG{INT} is
    defined to mean that the loop shall be left after having displayed the
    current item.

    Note: This command requires XML::LibXML installed.

    Note: This whole command currently is a bit klunky and will probably
    change in future versions of CPAN.pm but the general approach will
    likely stay.

    Note: See also smoke

  recompile
    recompile() is a very special command in that it takes no argument and
    runs the make/test/install cycle with brute force over all installed
    dynamically loadable extensions (aka XS modules) with 'force' in effect.
    The primary purpose of this command is to finish a network installation.
    Imagine, you have a common source tree for two different architectures.
    You decide to do a completely independent fresh installation. You start
    on one architecture with the help of a Bundle file produced earlier.
    CPAN installs the whole Bundle for you, but when you try to repeat the
    job on the second architecture, CPAN responds with a "Foo up to date"
    message for all modules. So you invoke CPAN's recompile on the second
    architecture and you're done.

    Another popular use for "recompile" is to act as a rescue in case your
    perl breaks binary compatibility. If one of the modules that CPAN uses
    is in turn depending on binary compatibility (so you cannot run CPAN
    commands), then you should try the CPAN::Nox module for recovery.

  report Bundle|Distribution|Module
    The "report" command temporarily turns on the "test_report" config
    variable, then runs the "force test" command with the given arguments.
    The "force" pragma is used to re-run the tests and repeat every step
    that might have failed before.

  smoke ***EXPERIMENTAL COMMAND***
    *** WARNING: this command downloads and executes software from CPAN to
    your computer of completely unknown status. You should never do this
    with your normal account and better have a dedicated well separated and
    secured machine to do this. ***

    The "smoke" command takes the list of recent uploads to CPAN as provided
    by the "recent" command and tests them all. While the command is running
    $SIG{INT} is defined to mean that the current item shall be skipped.

    Note: This whole command currently is a bit klunky and will probably
    change in future versions of CPAN.pm but the general approach will
    likely stay.

    Note: See also recent

  upgrade [Module|/Regex/]...
    The "upgrade" command first runs an "r" command with the given arguments
    and then installs the newest versions of all modules that were listed by
    that.

  The four "CPAN::*" Classes: Author, Bundle, Module, Distribution
    Although it may be considered internal, the class hierarchy does matter
    for both users and programmer. CPAN.pm deals with above mentioned four
    classes, and all those classes share a set of methods. A classical
    single polymorphism is in effect. A metaclass object registers all
    objects of all kinds and indexes them with a string. The strings
    referencing objects have a separated namespace (well, not completely
    separated):

             Namespace                         Class

       words containing a "/" (slash)      Distribution
        words starting with Bundle::          Bundle
              everything else            Module or Author

    Modules know their associated Distribution objects. They always refer to
    the most recent official release. Developers may mark their releases as
    unstable development versions (by inserting an underbar into the module
    version number which will also be reflected in the distribution name
    when you run 'make dist'), so the really hottest and newest distribution
    is not always the default. If a module Foo circulates on CPAN in both
    version 1.23 and 1.23_90, CPAN.pm offers a convenient way to install
    version 1.23 by saying

        install Foo

    This would install the complete distribution file (say
    BAR/Foo-1.23.tar.gz) with all accompanying material. But if you would
    like to install version 1.23_90, you need to know where the distribution
    file resides on CPAN relative to the authors/id/ directory. If the
    author is BAR, this might be BAR/Foo-1.23_90.tar.gz; so you would have
    to say

        install BAR/Foo-1.23_90.tar.gz

    The first example will be driven by an object of the class CPAN::Module,
    the second by an object of class CPAN::Distribution.

  Integrating local directories
    Note: this feature is still in alpha state and may change in future
    versions of CPAN.pm

    Distribution objects are normally distributions from the CPAN, but there
    is a slightly degenerate case for Distribution objects, too, of projects
    held on the local disk. These distribution objects have the same name as
    the local directory and end with a dot. A dot by itself is also allowed
    for the current directory at the time CPAN.pm was used. All actions such
    as "make", "test", and "install" are applied directly to that directory.
    This gives the command "cpan ." an interesting touch: while the normal
    mantra of installing a CPAN module without CPAN.pm is one of

        perl Makefile.PL                 perl Build.PL
               ( go and get prerequisites )
        make                             ./Build
        make test                        ./Build test
        make install                     ./Build install

    the command "cpan ." does all of this at once. It figures out which of
    the two mantras is appropriate, fetches and installs all prerequisites,
    cares for them recursively and finally finishes the installation of the
    module in the current directory, be it a CPAN module or not.

    The typical usage case is for private modules or working copies of
    projects from remote repositories on the local disk.

CONFIGURATION
    When the CPAN module is used for the first time, a configuration dialog
    tries to determine a couple of site specific options. The result of the
    dialog is stored in a hash reference $CPAN::Config in a file
    CPAN/Config.pm.

    The default values defined in the CPAN/Config.pm file can be overridden
    in a user specific file: CPAN/MyConfig.pm. Such a file is best placed in
    $HOME/.cpan/CPAN/MyConfig.pm, because $HOME/.cpan is added to the search
    path of the CPAN module before the use() or require() statements. The
    mkmyconfig command writes this file for you.

    The "o conf" command has various bells and whistles:

    completion support
        If you have a ReadLine module installed, you can hit TAB at any
        point of the commandline and "o conf" will offer you completion for
        the built-in subcommands and/or config variable names.

    displaying some help: o conf help
        Displays a short help

    displaying current values: o conf [KEY]
        Displays the current value(s) for this config variable. Without KEY
        displays all subcommands and config variables.

        Example:

          o conf shell

        If KEY starts and ends with a slash the string in between is
        interpreted as a regular expression and only keys matching this
        regex are displayed

        Example:

          o conf /color/

    changing of scalar values: o conf KEY VALUE
        Sets the config variable KEY to VALUE. The empty string can be
        specified as usual in shells, with '' or ""

        Example:

          o conf wget /usr/bin/wget

    changing of list values: o conf KEY SHIFT|UNSHIFT|PUSH|POP|SPLICE|LIST
        If a config variable name ends with "list", it is a list. "o conf
        KEY shift" removes the first element of the list, "o conf KEY pop"
        removes the last element of the list. "o conf KEYS unshift LIST"
        prepends a list of values to the list, "o conf KEYS push LIST"
        appends a list of valued to the list.

        Likewise, "o conf KEY splice LIST" passes the LIST to the according
        splice command.

        Finally, any other list of arguments is taken as a new list value
        for the KEY variable discarding the previous value.

        Examples:

          o conf urllist unshift http://cpan.dev.local/CPAN
          o conf urllist splice 3 1
          o conf urllist http://cpan1.local http://cpan2.local ftp://ftp.perl.org

    reverting to saved: o conf defaults
        Reverts all config variables to the state in the saved config file.

    saving the config: o conf commit
        Saves all config variables to the current config file
        (CPAN/Config.pm or CPAN/MyConfig.pm that was loaded at start).

    The configuration dialog can be started any time later again by issuing
    the command " o conf init " in the CPAN shell. A subset of the
    configuration dialog can be run by issuing "o conf init WORD" where WORD
    is any valid config variable or a regular expression.

  Config Variables
    Currently the following keys in the hash reference $CPAN::Config are
    defined:

      applypatch         path to external prg
      auto_commit        commit all changes to config variables to disk
      build_cache        size of cache for directories to build modules
      build_dir          locally accessible directory to build modules
      build_dir_reuse    boolean if distros in build_dir are persistent
      build_requires_install_policy
                         to install or not to install when a module is
                         only needed for building. yes|no|ask/yes|ask/no
      bzip2              path to external prg
      cache_metadata     use serializer to cache metadata
      commands_quote     prefered character to use for quoting external
                         commands when running them. Defaults to double
                         quote on Windows, single tick everywhere else;
                         can be set to space to disable quoting
      check_sigs         if signatures should be verified
      colorize_debug     Term::ANSIColor attributes for debugging output
      colorize_output    boolean if Term::ANSIColor should colorize output
      colorize_print     Term::ANSIColor attributes for normal output
      colorize_warn      Term::ANSIColor attributes for warnings
      commandnumber_in_prompt
                         boolean if you want to see current command number
      cpan_home          local directory reserved for this package
      curl               path to external prg
      dontload_hash      DEPRECATED
      dontload_list      arrayref: modules in the list will not be
                         loaded by the CPAN::has_inst() routine
      ftp                path to external prg
      ftp_passive        if set, the envariable FTP_PASSIVE is set for downloads
      ftp_proxy          proxy host for ftp requests
      getcwd             see below
      gpg                path to external prg
      gzip               location of external program gzip
      histfile           file to maintain history between sessions
      histsize           maximum number of lines to keep in histfile
      http_proxy         proxy host for http requests
      inactivity_timeout breaks interactive Makefile.PLs or Build.PLs
                         after this many seconds inactivity. Set to 0 to
                         never break.
      index_expire       after this many days refetch index files
      inhibit_startup_message
                         if true, does not print the startup message
      keep_source_where  directory in which to keep the source (if we do)
      load_module_verbosity
                         report loading of optional modules used by CPAN.pm
      lynx               path to external prg
      make               location of external make program
      make_arg           arguments that should always be passed to 'make'
      make_install_make_command
                         the make command for running 'make install', for
                         example 'sudo make'
      make_install_arg   same as make_arg for 'make install'
      makepl_arg         arguments passed to 'perl Makefile.PL'
      mbuild_arg         arguments passed to './Build'
      mbuild_install_arg arguments passed to './Build install'
      mbuild_install_build_command
                         command to use instead of './Build' when we are
                         in the install stage, for example 'sudo ./Build'
      mbuildpl_arg       arguments passed to 'perl Build.PL'
      ncftp              path to external prg
      ncftpget           path to external prg
      no_proxy           don't proxy to these hosts/domains (comma separated list)
      pager              location of external program more (or any pager)
      password           your password if you CPAN server wants one
      patch              path to external prg
      prefer_installer   legal values are MB and EUMM: if a module comes
                         with both a Makefile.PL and a Build.PL, use the
                         former (EUMM) or the latter (MB); if the module
                         comes with only one of the two, that one will be
                         used in any case
      prerequisites_policy
                         what to do if you are missing module prerequisites
                         ('follow' automatically, 'ask' me, or 'ignore')
      prefs_dir          local directory to store per-distro build options
      proxy_user         username for accessing an authenticating proxy
      proxy_pass         password for accessing an authenticating proxy
      randomize_urllist  add some randomness to the sequence of the urllist
      scan_cache         controls scanning of cache ('atstart' or 'never')
      shell              your favorite shell
      show_unparsable_versions
                         boolean if r command tells which modules are versionless
      show_upload_date   boolean if commands should try to determine upload date
      show_zero_versions boolean if r command tells for which modules $version==0
      tar                location of external program tar
      tar_verbosity      verbosity level for the tar command
      term_is_latin      deprecated: if true Unicode is translated to ISO-8859-1
                         (and nonsense for characters outside latin range)
      term_ornaments     boolean to turn ReadLine ornamenting on/off
      test_report        email test reports (if CPAN::Reporter is installed)
      unzip              location of external program unzip
      urllist            arrayref to nearby CPAN sites (or equivalent locations)
      use_sqlite         use CPAN::SQLite for metadata storage (fast and lean)
      username           your username if you CPAN server wants one
      wait_list          arrayref to a wait server to try (See CPAN::WAIT)
      wget               path to external prg
      yaml_load_code     enable YAML code deserialisation
      yaml_module        which module to use to read/write YAML files

    You can set and query each of these options interactively in the cpan
    shell with the "o conf" or the "o conf init" command as specified below.

    "o conf <scalar option>"
      prints the current value of the *scalar option*

    "o conf <scalar option> <value>"
      Sets the value of the *scalar option* to *value*

    "o conf <list option>"
      prints the current value of the *list option* in MakeMaker's neatvalue
      format.

    "o conf <list option> [shift|pop]"
      shifts or pops the array in the *list option* variable

    "o conf <list option> [unshift|push|splice] <list>"
      works like the corresponding perl commands.

    interactive editing: o conf init [MATCH|LIST]
      Runs an interactive configuration dialog for matching variables.
      Without argument runs the dialog over all supported config variables.
      To specify a MATCH the argument must be enclosed by slashes.

      Examples:

        o conf init ftp_passive ftp_proxy
        o conf init /color/

      Note: this method of setting config variables often provides more
      explanation about the functioning of a variable than the manpage.

  CPAN::anycwd($path): Note on config variable getcwd
    CPAN.pm changes the current working directory often and needs to
    determine its own current working directory. Per default it uses
    Cwd::cwd but if this doesn't work on your system for some reason,
    alternatives can be configured according to the following table:

    cwd Calls Cwd::cwd

    getcwd
        Calls Cwd::getcwd

    fastcwd
        Calls Cwd::fastcwd

    backtickcwd
        Calls the external command cwd.

  Note on the format of the urllist parameter
    urllist parameters are URLs according to RFC 1738. We do a little
    guessing if your URL is not compliant, but if you have problems with
    "file" URLs, please try the correct format. Either:

        file://localhost/whatever/ftp/pub/CPAN/

    or

        file:///home/ftp/pub/CPAN/

  The urllist parameter has CD-ROM support
    The "urllist" parameter of the configuration table contains a list of
    URLs that are to be used for downloading. If the list contains any
    "file" URLs, CPAN always tries to get files from there first. This
    feature is disabled for index files. So the recommendation for the owner
    of a CD-ROM with CPAN contents is: include your local, possibly outdated
    CD-ROM as a "file" URL at the end of urllist, e.g.

      o conf urllist push file://localhost/CDROM/CPAN

    CPAN.pm will then fetch the index files from one of the CPAN sites that
    come at the beginning of urllist. It will later check for each module if
    there is a local copy of the most recent version.

    Another peculiarity of urllist is that the site that we could
    successfully fetch the last file from automatically gets a preference
    token and is tried as the first site for the next request. So if you add
    a new site at runtime it may happen that the previously preferred site
    will be tried another time. This means that if you want to disallow a
    site for the next transfer, it must be explicitly removed from urllist.

  Maintaining the urllist parameter
    If you have YAML.pm (or some other YAML module configured in
    "yaml_module") installed, CPAN.pm collects a few statistical data about
    recent downloads. You can view the statistics with the "hosts" command
    or inspect them directly by looking into the "FTPstats.yml" file in your
    "cpan_home" directory.

    To get some interesting statistics it is recommended to set the
    "randomize_urllist" parameter that introduces some amount of randomness
    into the URL selection.

  The "requires" and "build_requires" dependency declarations
    Since CPAN.pm version 1.88_51 modules declared as "build_requires" by a
    distribution are treated differently depending on the config variable
    "build_requires_install_policy". By setting
    "build_requires_install_policy" to "no" such a module is not being
    installed. It is only built and tested and then kept in the list of
    tested but uninstalled modules. As such it is available during the build
    of the dependent module by integrating the path to the "blib/arch" and
    "blib/lib" directories in the environment variable PERL5LIB. If
    "build_requires_install_policy" is set ti "yes", then both modules
    declared as "requires" and those declared as "build_requires" are
    treated alike. By setting to "ask/yes" or "ask/no", CPAN.pm asks the
    user and sets the default accordingly.

  Configuration for individual distributions (*Distroprefs*)
    (Note: This feature has been introduced in CPAN.pm 1.8854 and is still
    considered beta quality)

    Distributions on the CPAN usually behave according to what we call the
    CPAN mantra. Or since the event of Module::Build we should talk about
    two mantras:

        perl Makefile.PL     perl Build.PL
        make                 ./Build
        make test            ./Build test
        make install         ./Build install

    But some modules cannot be built with this mantra. They try to get some
    extra data from the user via the environment, extra arguments or
    interactively thus disturbing the installation of large bundles like
    Phalanx100 or modules with many dependencies like Plagger.

    The distroprefs system of "CPAN.pm" addresses this problem by allowing
    the user to specify extra informations and recipes in YAML files to
    either

    *   pass additional arguments to one of the four commands,

    *   set environment variables

    *   instantiate an Expect object that reads from the console, waits for
        some regular expressions and enters some answers

    *   temporarily override assorted "CPAN.pm" configuration variables

    *   specify dependencies that the original maintainer forgot to specify

    *   disable the installation of an object altogether

    See the YAML and Data::Dumper files that come with the "CPAN.pm"
    distribution in the "distroprefs/" directory for examples.

  Filenames
    The YAML files themselves must have the ".yml" extension, all other
    files are ignored (for two exceptions see *Fallback Data::Dumper and
    Storable* below). The containing directory can be specified in "CPAN.pm"
    in the "prefs_dir" config variable. Try "o conf init prefs_dir" in the
    CPAN shell to set and activate the distroprefs system.

    Every YAML file may contain arbitrary documents according to the YAML
    specification and every single document is treated as an entity that can
    specify the treatment of a single distribution.

    The names of the files can be picked freely, "CPAN.pm" always reads all
    files (in alphabetical order) and takes the key "match" (see below in
    *Language Specs*) as a hashref containing match criteria that determine
    if the current distribution matches the YAML document or not.

  Fallback Data::Dumper and Storable
    If neither your configured "yaml_module" nor YAML.pm is installed
    CPAN.pm falls back to using Data::Dumper and Storable and looks for
    files with the extensions ".dd" or ".st" in the "prefs_dir" directory.
    These files are expected to contain one or more hashrefs. For
    Data::Dumper generated files, this is expected to be done with by
    defining $VAR1, $VAR2, etc. The YAML shell would produce these with the
    command

        ysh < somefile.yml > somefile.dd

    For Storable files the rule is that they must be constructed such that
    "Storable::retrieve(file)" returns an array reference and the array
    elements represent one distropref object each. The conversion from YAML
    would look like so:

        perl -MYAML=LoadFile -MStorable=nstore -e '
            @y=LoadFile(shift);
            nstore(\@y, shift)' somefile.yml somefile.st

    In bootstrapping situations it is usually sufficient to translate only a
    few YAML files to Data::Dumper for the crucial modules like
    "YAML::Syck", "YAML.pm" and "Expect.pm". If you prefer Storable over
    Data::Dumper, remember to pull out a Storable version that writes an
    older format than all the other Storable versions that will need to read
    them.

  Blueprint
    The following example contains all supported keywords and structures
    with the exception of "eexpect" which can be used instead of "expect".

      ---
      comment: "Demo"
      match:
        module: "Dancing::Queen"
        distribution: "^CHACHACHA/Dancing-"
        perl: "/usr/local/cariba-perl/bin/perl"
        perlconfig:
          archname: "freebsd"
      disabled: 1
      cpanconfig:
        make: gmake
      pl:
        args:
          - "--somearg=specialcase"

        env: {}

        expect:
          - "Which is your favorite fruit"
          - "apple\n"

      make:
        args:
          - all
          - extra-all

        env: {}

        expect: []

        commendline: "echo SKIPPING make"

      test:
        args: []

        env: {}

        expect: []

      install:
        args: []

        env:
          WANT_TO_INSTALL: YES

        expect:
          - "Do you really want to install"
          - "y\n"

      patches:
        - "ABCDE/Fedcba-3.14-ABCDE-01.patch"

      depends:
        configure_requires:
          LWP: 5.8
        build_requires:
          Test::Exception: 0.25
        requires:
          Spiffy: 0.30

  Language Specs
    Every YAML document represents a single hash reference. The valid keys
    in this hash are as follows:

    comment [scalar]
        A comment

    cpanconfig [hash]
        Temporarily override assorted "CPAN.pm" configuration variables.

        Supported are: "build_requires_install_policy", "check_sigs",
        "make", "make_install_make_command", "prefer_installer",
        "test_report". Please report as a bug when you need another one
        supported.

    depends [hash] *** EXPERIMENTAL FEATURE ***
        All three types, namely "configure_requires", "build_requires", and
        "requires" are supported in the way specified in the META.yml
        specification. The current implementation *merges* the specified
        dependencies with those declared by the package maintainer. In a
        future implementation this may be changed to override the original
        declaration.

    disabled [boolean]
        Specifies that this distribution shall not be processed at all.

    goto [string]
        The canonical name of a delegate distribution that shall be
        installed instead. Useful when a new version, although it tests OK
        itself, breaks something else or a developer release or a fork is
        already uploaded that is better than the last released version.

    install [hash]
        Processing instructions for the "make install" or "./Build install"
        phase of the CPAN mantra. See below under *Processiong
        Instructions*.

    make [hash]
        Processing instructions for the "make" or "./Build" phase of the
        CPAN mantra. See below under *Processiong Instructions*.

    match [hash]
        A hashref with one or more of the keys "distribution", "modules",
        "perl", and "perlconfig" that specify if a document is targeted at a
        specific CPAN distribution or installation.

        The corresponding values are interpreted as regular expressions. The
        "distribution" related one will be matched against the canonical
        distribution name, e.g. "AUTHOR/Foo-Bar-3.14.tar.gz".

        The "module" related one will be matched against *all* modules
        contained in the distribution until one module matches.

        The "perl" related one will be matched against $^X (but with the
        absolute path).

        The value associated with "perlconfig" is itself a hashref that is
        matched against corresponding values in the %Config::Config hash
        living in the " Config.pm " module.

        If more than one restriction of "module", "distribution", and "perl"
        is specified, the results of the separately computed match values
        must all match. If this is the case then the hashref represented by
        the YAML document is returned as the preference structure for the
        current distribution.

    patches [array]
        An array of patches on CPAN or on the local disk to be applied in
        order via the external patch program. If the value for the "-p"
        parameter is 0 or 1 is determined by reading the patch beforehand.

        Note: if the "applypatch" program is installed and "CPAN::Config"
        knows about it and a patch is written by the "makepatch" program,
        then "CPAN.pm" lets "applypatch" apply the patch. Both "makepatch"
        and "applypatch" are available from CPAN in the "JV/makepatch-*"
        distribution.

    pl [hash]
        Processing instructions for the "perl Makefile.PL" or "perl
        Build.PL" phase of the CPAN mantra. See below under *Processiong
        Instructions*.

    test [hash]
        Processing instructions for the "make test" or "./Build test" phase
        of the CPAN mantra. See below under *Processiong Instructions*.

  Processing Instructions
    args [array]
        Arguments to be added to the command line

    commandline
        A full commandline that will be executed as it stands by a system
        call. During the execution the environment variable PERL will is set
        to $^X (but with an absolute path). If "commandline" is specified,
        the content of "args" is not used.

    eexpect [hash]
        Extended "expect". This is a hash reference with four allowed keys,
        "mode", "timeout", "reuse", and "talk".

        "mode" may have the values "deterministic" for the case where all
        questions come in the order written down and "anyorder" for the case
        where the questions may come in any order. The default mode is
        "deterministic".

        "timeout" denotes a timeout in seconds. Floating point timeouts are
        OK. In the case of a "mode=deterministic" the timeout denotes the
        timeout per question, in the case of "mode=anyorder" it denotes the
        timeout per byte received from the stream or questions.

        "talk" is a reference to an array that contains alternating
        questions and answers. Questions are regular expressions and answers
        are literal strings. The Expect module will then watch the stream
        coming from the execution of the external program ("perl
        Makefile.PL", "perl Build.PL", "make", etc.).

        In the case of "mode=deterministic" the CPAN.pm will inject the
        according answer as soon as the stream matches the regular
        expression.

        In the case of "mode=anyorder" CPAN.pm will answer a question as
        soon as the timeout is reached for the next byte in the input
        stream. In this mode you can use the "reuse" parameter to decide
        what shall happen with a question-answer pair after it has been
        used. In the default case (reuse=0) it is removed from the array, so
        it cannot be used again accidentally. In this case, if you want to
        answer the question "Do you really want to do that" several times,
        then it must be included in the array at least as often as you want
        this answer to be given. Setting the parameter "reuse" to 1 makes
        this repetition unnecessary.

    env [hash]
        Environment variables to be set during the command

    expect [array]
        "expect: <array>" is a short notation for

          eexpect:
            mode: deterministic
            timeout: 15
            talk: <array>

  Schema verification with "Kwalify"
    If you have the "Kwalify" module installed (which is part of the
    Bundle::CPANxxl), then all your distroprefs files are checked for
    syntactical correctness.

  Example Distroprefs Files
    "CPAN.pm" comes with a collection of example YAML files. Note that these
    are really just examples and should not be used without care because
    they cannot fit everybody's purpose. After all the authors of the
    packages that ask questions had a need to ask, so you should watch their
    questions and adjust the examples to your environment and your needs.
    You have beend warned:-)

PROGRAMMER'S INTERFACE
    If you do not enter the shell, the available shell commands are both
    available as methods ("CPAN::Shell->install(...)") and as functions in
    the calling package ("install(...)"). Before calling low-level commands
    it makes sense to initialize components of CPAN you need, e.g.:

      CPAN::HandleConfig->load;
      CPAN::Shell::setup_output;
      CPAN::Index->reload;

    High-level commands do such initializations automatically.

    There's currently only one class that has a stable interface -
    CPAN::Shell. All commands that are available in the CPAN shell are
    methods of the class CPAN::Shell. Each of the commands that produce
    listings of modules ("r", "autobundle", "u") also return a list of the
    IDs of all modules within the list.

    expand($type,@things)
      The IDs of all objects available within a program are strings that can
      be expanded to the corresponding real objects with the
      "CPAN::Shell->expand("Module",@things)" method. Expand returns a list
      of CPAN::Module objects according to the @things arguments given. In
      scalar context it only returns the first element of the list.

    expandany(@things)
      Like expand, but returns objects of the appropriate type, i.e.
      CPAN::Bundle objects for bundles, CPAN::Module objects for modules and
      CPAN::Distribution objects for distributions. Note: it does not expand
      to CPAN::Author objects.

    Programming Examples
      This enables the programmer to do operations that combine
      functionalities that are available in the shell.

          # install everything that is outdated on my disk:
          perl -MCPAN -e 'CPAN::Shell->install(CPAN::Shell->r)'

          # install my favorite programs if necessary:
          for $mod (qw(Net::FTP Digest::SHA Data::Dumper)) {
              CPAN::Shell->install($mod);
          }

          # list all modules on my disk that have no VERSION number
          for $mod (CPAN::Shell->expand("Module","/./")) {
              next unless $mod->inst_file;
              # MakeMaker convention for undefined $VERSION:
              next unless $mod->inst_version eq "undef";
              print "No VERSION in ", $mod->id, "\n";
          }

          # find out which distribution on CPAN contains a module:
          print CPAN::Shell->expand("Module","Apache::Constants")->cpan_file

      Or if you want to write a cronjob to watch The CPAN, you could list
      all modules that need updating. First a quick and dirty way:

          perl -e 'use CPAN; CPAN::Shell->r;'

      If you don't want to get any output in the case that all modules are
      up to date, you can parse the output of above command for the regular
      expression //modules are up to date// and decide to mail the output
      only if it doesn't match. Ick?

      If you prefer to do it more in a programmer style in one single
      process, maybe something like this suits you better:

        # list all modules on my disk that have newer versions on CPAN
        for $mod (CPAN::Shell->expand("Module","/./")) {
          next unless $mod->inst_file;
          next if $mod->uptodate;
          printf "Module %s is installed as %s, could be updated to %s from CPAN\n",
              $mod->id, $mod->inst_version, $mod->cpan_version;
        }

      If that gives you too much output every day, you maybe only want to
      watch for three modules. You can write

        for $mod (CPAN::Shell->expand("Module","/Apache|LWP|CGI/")) {

      as the first line instead. Or you can combine some of the above
      tricks:

        # watch only for a new mod_perl module
        $mod = CPAN::Shell->expand("Module","mod_perl");
        exit if $mod->uptodate;
        # new mod_perl arrived, let me know all update recommendations
        CPAN::Shell->r;

  Methods in the other Classes
    CPAN::Author::as_glimpse()
        Returns a one-line description of the author

    CPAN::Author::as_string()
        Returns a multi-line description of the author

    CPAN::Author::email()
        Returns the author's email address

    CPAN::Author::fullname()
        Returns the author's name

    CPAN::Author::name()
        An alias for fullname

    CPAN::Bundle::as_glimpse()
        Returns a one-line description of the bundle

    CPAN::Bundle::as_string()
        Returns a multi-line description of the bundle

    CPAN::Bundle::clean()
        Recursively runs the "clean" method on all items contained in the
        bundle.

    CPAN::Bundle::contains()
        Returns a list of objects' IDs contained in a bundle. The associated
        objects may be bundles, modules or distributions.

    CPAN::Bundle::force($method,@args)
        Forces CPAN to perform a task that it normally would have refused to
        do. Force takes as arguments a method name to be called and any
        number of additional arguments that should be passed to the called
        method. The internals of the object get the needed changes so that
        CPAN.pm does not refuse to take the action. The "force" is passed
        recursively to all contained objects. See also the section above on
        the "force" and the "fforce" pragma.

    CPAN::Bundle::get()
        Recursively runs the "get" method on all items contained in the
        bundle

    CPAN::Bundle::inst_file()
        Returns the highest installed version of the bundle in either @INC
        or "$CPAN::Config-"{cpan_home}>. Note that this is different from
        CPAN::Module::inst_file.

    CPAN::Bundle::inst_version()
        Like CPAN::Bundle::inst_file, but returns the $VERSION

    CPAN::Bundle::uptodate()
        Returns 1 if the bundle itself and all its members are uptodate.

    CPAN::Bundle::install()
        Recursively runs the "install" method on all items contained in the
        bundle

    CPAN::Bundle::make()
        Recursively runs the "make" method on all items contained in the
        bundle

    CPAN::Bundle::readme()
        Recursively runs the "readme" method on all items contained in the
        bundle

    CPAN::Bundle::test()
        Recursively runs the "test" method on all items contained in the
        bundle

    CPAN::Distribution::as_glimpse()
        Returns a one-line description of the distribution

    CPAN::Distribution::as_string()
        Returns a multi-line description of the distribution

    CPAN::Distribution::author
        Returns the CPAN::Author object of the maintainer who uploaded this
        distribution

    CPAN::Distribution::pretty_id()
        Returns a string of the form "AUTHORID/TARBALL", where AUTHORID is
        the author's PAUSE ID and TARBALL is the distribution filename.

    CPAN::Distribution::base_id()
        Returns the distribution filename without any archive suffix. E.g
        "Foo-Bar-0.01"

    CPAN::Distribution::clean()
        Changes to the directory where the distribution has been unpacked
        and runs "make clean" there.

    CPAN::Distribution::containsmods()
        Returns a list of IDs of modules contained in a distribution file.
        Only works for distributions listed in the 02packages.details.txt.gz
        file. This typically means that only the most recent version of a
        distribution is covered.

    CPAN::Distribution::cvs_import()
        Changes to the directory where the distribution has been unpacked
        and runs something like

            cvs -d $cvs_root import -m $cvs_log $cvs_dir $userid v$version

        there.

    CPAN::Distribution::dir()
        Returns the directory into which this distribution has been
        unpacked.

    CPAN::Distribution::force($method,@args)
        Forces CPAN to perform a task that it normally would have refused to
        do. Force takes as arguments a method name to be called and any
        number of additional arguments that should be passed to the called
        method. The internals of the object get the needed changes so that
        CPAN.pm does not refuse to take the action. See also the section
        above on the "force" and the "fforce" pragma.

    CPAN::Distribution::get()
        Downloads the distribution from CPAN and unpacks it. Does nothing if
        the distribution has already been downloaded and unpacked within the
        current session.

    CPAN::Distribution::install()
        Changes to the directory where the distribution has been unpacked
        and runs the external command "make install" there. If "make" has
        not yet been run, it will be run first. A "make test" will be issued
        in any case and if this fails, the install will be canceled. The
        cancellation can be avoided by letting "force" run the "install" for
        you.

        This install method has only the power to install the distribution
        if there are no dependencies in the way. To install an object and
        all of its dependencies, use CPAN::Shell->install.

        Note that install() gives no meaningful return value. See
        uptodate().

    CPAN::Distribution::install_tested()
        Install all the distributions that have been tested sucessfully but
        not yet installed. See also "is_tested".

    CPAN::Distribution::isa_perl()
        Returns 1 if this distribution file seems to be a perl distribution.
        Normally this is derived from the file name only, but the index from
        CPAN can contain a hint to achieve a return value of true for other
        filenames too.

    CPAN::Distribution::is_tested()
        List all the distributions that have been tested sucessfully but not
        yet installed. See also "install_tested".

    CPAN::Distribution::look()
        Changes to the directory where the distribution has been unpacked
        and opens a subshell there. Exiting the subshell returns.

    CPAN::Distribution::make()
        First runs the "get" method to make sure the distribution is
        downloaded and unpacked. Changes to the directory where the
        distribution has been unpacked and runs the external commands "perl
        Makefile.PL" or "perl Build.PL" and "make" there.

    CPAN::Distribution::perldoc()
        Downloads the pod documentation of the file associated with a
        distribution (in html format) and runs it through the external
        command lynx specified in "$CPAN::Config-"{lynx}>. If lynx isn't
        available, it converts it to plain text with external command
        html2text and runs it through the pager specified in
        "$CPAN::Config-"{pager}>

    CPAN::Distribution::prefs()
        Returns the hash reference from the first matching YAML file that
        the user has deposited in the "prefs_dir/" directory. The first
        succeeding match wins. The files in the "prefs_dir/" are processed
        alphabetically and the canonical distroname (e.g.
        AUTHOR/Foo-Bar-3.14.tar.gz) is matched against the regular
        expressions stored in the $root->{match}{distribution} attribute
        value. Additionally all module names contained in a distribution are
        matched agains the regular expressions in the $root->{match}{module}
        attribute value. The two match values are ANDed together. Each of
        the two attributes are optional.

    CPAN::Distribution::prereq_pm()
        Returns the hash reference that has been announced by a distribution
        as the the "requires" and "build_requires" elements. These can be
        declared either by the "META.yml" (if authoritative) or can be
        deposited after the run of "Build.PL" in the file "./_build/prereqs"
        or after the run of "Makfile.PL" written as the "PREREQ_PM" hash in
        a comment in the produced "Makefile". *Note*: this method only works
        after an attempt has been made to "make" the distribution. Returns
        undef otherwise.

    CPAN::Distribution::readme()
        Downloads the README file associated with a distribution and runs it
        through the pager specified in "$CPAN::Config-"{pager}>.

    CPAN::Distribution::reports()
        Downloads report data for this distribution from
        cpantesters.perl.org and displays a subset of them.

    CPAN::Distribution::read_yaml()
        Returns the content of the META.yml of this distro as a hashref.
        Note: works only after an attempt has been made to "make" the
        distribution. Returns undef otherwise. Also returns undef if the
        content of META.yml is not authoritative. (The rules about what
        exactly makes the content authoritative are still in flux.)

    CPAN::Distribution::test()
        Changes to the directory where the distribution has been unpacked
        and runs "make test" there.

    CPAN::Distribution::uptodate()
        Returns 1 if all the modules contained in the distribution are
        uptodate. Relies on containsmods.

    CPAN::Index::force_reload()
        Forces a reload of all indices.

    CPAN::Index::reload()
        Reloads all indices if they have not been read for more than
        "$CPAN::Config-"{index_expire}> days.

    CPAN::InfoObj::dump()
        CPAN::Author, CPAN::Bundle, CPAN::Module, and CPAN::Distribution
        inherit this method. It prints the data structure associated with an
        object. Useful for debugging. Note: the data structure is considered
        internal and thus subject to change without notice.

    CPAN::Module::as_glimpse()
        Returns a one-line description of the module in four columns: The
        first column contains the word "Module", the second column consists
        of one character: an equals sign if this module is already installed
        and uptodate, a less-than sign if this module is installed but can
        be upgraded, and a space if the module is not installed. The third
        column is the name of the module and the fourth column gives
        maintainer or distribution information.

    CPAN::Module::as_string()
        Returns a multi-line description of the module

    CPAN::Module::clean()
        Runs a clean on the distribution associated with this module.

    CPAN::Module::cpan_file()
        Returns the filename on CPAN that is associated with the module.

    CPAN::Module::cpan_version()
        Returns the latest version of this module available on CPAN.

    CPAN::Module::cvs_import()
        Runs a cvs_import on the distribution associated with this module.

    CPAN::Module::description()
        Returns a 44 character description of this module. Only available
        for modules listed in The Module List
        (CPAN/modules/00modlist.long.html or 00modlist.long.txt.gz)

    CPAN::Module::distribution()
        Returns the CPAN::Distribution object that contains the current
        version of this module.

    CPAN::Module::dslip_status()
        Returns a hash reference. The keys of the hash are the letters "D",
        "S", "L", "I", and <P>, for development status, support level,
        language, interface and public licence respectively. The data for
        the DSLIP status are collected by pause.perl.org when authors
        register their namespaces. The values of the 5 hash elements are
        one-character words whose meaning is described in the table below.
        There are also 5 hash elements "DV", "SV", "LV", "IV", and <PV> that
        carry a more verbose value of the 5 status variables.

        Where the 'DSLIP' characters have the following meanings:

          D - Development Stage  (Note: *NO IMPLIED TIMESCALES*):
            i   - Idea, listed to gain consensus or as a placeholder
            c   - under construction but pre-alpha (not yet released)
            a/b - Alpha/Beta testing
            R   - Released
            M   - Mature (no rigorous definition)
            S   - Standard, supplied with Perl 5

          S - Support Level:
            m   - Mailing-list
            d   - Developer
            u   - Usenet newsgroup comp.lang.perl.modules
            n   - None known, try comp.lang.perl.modules
            a   - abandoned; volunteers welcome to take over maintainance

          L - Language Used:
            p   - Perl-only, no compiler needed, should be platform independent
            c   - C and perl, a C compiler will be needed
            h   - Hybrid, written in perl with optional C code, no compiler needed
            +   - C++ and perl, a C++ compiler will be needed
            o   - perl and another language other than C or C++

          I - Interface Style
            f   - plain Functions, no references used
            h   - hybrid, object and function interfaces available
            n   - no interface at all (huh?)
            r   - some use of unblessed References or ties
            O   - Object oriented using blessed references and/or inheritance

          P - Public License
            p   - Standard-Perl: user may choose between GPL and Artistic
            g   - GPL: GNU General Public License
            l   - LGPL: "GNU Lesser General Public License" (previously known as
                  "GNU Library General Public License")
            b   - BSD: The BSD License
            a   - Artistic license alone
            2   - Artistic license 2.0 or later
            o   - open source: appoved by www.opensource.org
            d   - allows distribution without restrictions
            r   - restricted distribtion
            n   - no license at all

    CPAN::Module::force($method,@args)
        Forces CPAN to perform a task that it normally would have refused to
        do. Force takes as arguments a method name to be called and any
        number of additional arguments that should be passed to the called
        method. The internals of the object get the needed changes so that
        CPAN.pm does not refuse to take the action. See also the section
        above on the "force" and the "fforce" pragma.

    CPAN::Module::get()
        Runs a get on the distribution associated with this module.

    CPAN::Module::inst_file()
        Returns the filename of the module found in @INC. The first file
        found is reported just like perl itself stops searching @INC when it
        finds a module.

    CPAN::Module::available_file()
        Returns the filename of the module found in PERL5LIB or @INC. The
        first file found is reported. The advantage of this method over
        "inst_file" is that modules that have been tested but not yet
        installed are included because PERL5LIB keeps track of tested
        modules.

    CPAN::Module::inst_version()
        Returns the version number of the installed module in readable
        format.

    CPAN::Module::available_version()
        Returns the version number of the available module in readable
        format.

    CPAN::Module::install()
        Runs an "install" on the distribution associated with this module.

    CPAN::Module::look()
        Changes to the directory where the distribution associated with this
        module has been unpacked and opens a subshell there. Exiting the
        subshell returns.

    CPAN::Module::make()
        Runs a "make" on the distribution associated with this module.

    CPAN::Module::manpage_headline()
        If module is installed, peeks into the module's manpage, reads the
        headline and returns it. Moreover, if the module has been downloaded
        within this session, does the equivalent on the downloaded module
        even if it is not installed.

    CPAN::Module::perldoc()
        Runs a "perldoc" on this module.

    CPAN::Module::readme()
        Runs a "readme" on the distribution associated with this module.

    CPAN::Module::reports()
        Calls the reports() method on the associated distribution object.

    CPAN::Module::test()
        Runs a "test" on the distribution associated with this module.

    CPAN::Module::uptodate()
        Returns 1 if the module is installed and up-to-date.

    CPAN::Module::userid()
        Returns the author's ID of the module.

  Cache Manager
    Currently the cache manager only keeps track of the build directory
    ($CPAN::Config->{build_dir}). It is a simple FIFO mechanism that deletes
    complete directories below "build_dir" as soon as the size of all
    directories there gets bigger than $CPAN::Config->{build_cache} (in MB).
    The contents of this cache may be used for later re-installations that
    you intend to do manually, but will never be trusted by CPAN itself.
    This is due to the fact that the user might use these directories for
    building modules on different architectures.

    There is another directory ($CPAN::Config->{keep_source_where}) where
    the original distribution files are kept. This directory is not covered
    by the cache manager and must be controlled by the user. If you choose
    to have the same directory as build_dir and as keep_source_where
    directory, then your sources will be deleted with the same fifo
    mechanism.

  Bundles
    A bundle is just a perl module in the namespace Bundle:: that does not
    define any functions or methods. It usually only contains documentation.

    It starts like a perl module with a package declaration and a $VERSION
    variable. After that the pod section looks like any other pod with the
    only difference being that *one special pod section* exists starting
    with (verbatim):

        =head1 CONTENTS

    In this pod section each line obeys the format

            Module_Name [Version_String] [- optional text]

    The only required part is the first field, the name of a module (e.g.
    Foo::Bar, ie. *not* the name of the distribution file). The rest of the
    line is optional. The comment part is delimited by a dash just as in the
    man page header.

    The distribution of a bundle should follow the same convention as other
    distributions.

    Bundles are treated specially in the CPAN package. If you say 'install
    Bundle::Tkkit' (assuming such a bundle exists), CPAN will install all
    the modules in the CONTENTS section of the pod. You can install your own
    Bundles locally by placing a conformant Bundle file somewhere into your
    @INC path. The autobundle() command which is available in the shell
    interface does that for you by including all currently installed modules
    in a snapshot bundle file.

PREREQUISITES
    If you have a local mirror of CPAN and can access all files with "file:"
    URLs, then you only need a perl better than perl5.003 to run this
    module. Otherwise Net::FTP is strongly recommended. LWP may be required
    for non-UNIX systems or if your nearest CPAN site is associated with a
    URL that is not "ftp:".

    If you have neither Net::FTP nor LWP, there is a fallback mechanism
    implemented for an external ftp command or for an external lynx command.

UTILITIES
  Finding packages and VERSION
    This module presumes that all packages on CPAN

    * declare their $VERSION variable in an easy to parse manner. This
      prerequisite can hardly be relaxed because it consumes far too much
      memory to load all packages into the running program just to determine
      the $VERSION variable. Currently all programs that are dealing with
      version use something like this

          perl -MExtUtils::MakeMaker -le \
              'print MM->parse_version(shift)' filename

      If you are author of a package and wonder if your $VERSION can be
      parsed, please try the above method.

    * come as compressed or gzipped tarfiles or as zip files and contain a
      "Makefile.PL" or "Build.PL" (well, we try to handle a bit more, but
      without much enthusiasm).

  Debugging
    The debugging of this module is a bit complex, because we have
    interferences of the software producing the indices on CPAN, of the
    mirroring process on CPAN, of packaging, of configuration, of
    synchronicity, and of bugs within CPAN.pm.

    For debugging the code of CPAN.pm itself in interactive mode some more
    or less useful debugging aid can be turned on for most packages within
    CPAN.pm with one of

    o debug package...
      sets debug mode for packages.

    o debug -package...
      unsets debug mode for packages.

    o debug all
      turns debugging on for all packages.

    o debug number

    which sets the debugging packages directly. Note that "o debug 0" turns
    debugging off.

    What seems quite a successful strategy is the combination of "reload
    cpan" and the debugging switches. Add a new debug statement while
    running in the shell and then issue a "reload cpan" and see the new
    debugging messages immediately without losing the current context.

    "o debug" without an argument lists the valid package names and the
    current set of packages in debugging mode. "o debug" has built-in
    completion support.

    For debugging of CPAN data there is the "dump" command which takes the
    same arguments as make/test/install and outputs each object's
    Data::Dumper dump. If an argument looks like a perl variable and
    contains one of "$", "@" or "%", it is eval()ed and fed to Data::Dumper
    directly.

  Floppy, Zip, Offline Mode
    CPAN.pm works nicely without network too. If you maintain machines that
    are not networked at all, you should consider working with file: URLs.
    Of course, you have to collect your modules somewhere first. So you
    might use CPAN.pm to put together all you need on a networked machine.
    Then copy the $CPAN::Config->{keep_source_where} (but not
    $CPAN::Config->{build_dir}) directory on a floppy. This floppy is kind
    of a personal CPAN. CPAN.pm on the non-networked machines works nicely
    with this floppy. See also below the paragraph about CD-ROM support.

  Basic Utilities for Programmers
    has_inst($module)
      Returns true if the module is installed. Used to load all modules into
      the running CPAN.pm which are considered optional. The config variable
      "dontload_list" can be used to intercept the "has_inst()" call such
      that an optional module is not loaded despite being available. For
      example the following command will prevent that "YAML.pm" is being
      loaded:

          cpan> o conf dontload_list push YAML

      See the source for details.

    has_usable($module)
      Returns true if the module is installed and is in a usable state. Only
      useful for a handful of modules that are used internally. See the
      source for details.

    instance($module)
      The constructor for all the singletons used to represent modules,
      distributions, authors and bundles. If the object already exists, this
      method returns the object, otherwise it calls the constructor.

SECURITY
    There's no strong security layer in CPAN.pm. CPAN.pm helps you to
    install foreign, unmasked, unsigned code on your machine. We compare to
    a checksum that comes from the net just as the distribution file itself.
    But we try to make it easy to add security on demand:

  Cryptographically signed modules
    Since release 1.77 CPAN.pm has been able to verify cryptographically
    signed module distributions using Module::Signature. The CPAN modules
    can be signed by their authors, thus giving more security. The simple
    unsigned MD5 checksums that were used before by CPAN protect mainly
    against accidental file corruption.

    You will need to have Module::Signature installed, which in turn
    requires that you have at least one of Crypt::OpenPGP module or the
    command-line gpg tool installed.

    You will also need to be able to connect over the Internet to the public
    keyservers, like pgp.mit.edu, and their port 11731 (the HKP protocol).

    The configuration parameter check_sigs is there to turn signature
    checking on or off.

EXPORT
    Most functions in package CPAN are exported per default. The reason for
    this is that the primary use is intended for the cpan shell or for
    one-liners.

ENVIRONMENT
    When the CPAN shell enters a subshell via the look command, it sets the
    environment CPAN_SHELL_LEVEL to 1 or increments it if it is already set.

    When CPAN runs, it sets the environment variable PERL5_CPAN_IS_RUNNING
    to the ID of the running process. It also sets PERL5_CPANPLUS_IS_RUNNING
    to prevent runaway processes which could happen with older versions of
    Module::Install.

    When running "perl Makefile.PL", the environment variable
    "PERL5_CPAN_IS_EXECUTING" is set to the full path of the "Makefile.PL"
    that is being executed. This prevents runaway processes with newer
    versions of Module::Install.

    When the config variable ftp_passive is set, all downloads will be run
    with the environment variable FTP_PASSIVE set to this value. This is in
    general a good idea as it influences both Net::FTP and LWP based
    connections. The same effect can be achieved by starting the cpan shell
    with this environment variable set. For Net::FTP alone, one can also
    always set passive mode by running libnetcfg.

POPULATE AN INSTALLATION WITH LOTS OF MODULES
    Populating a freshly installed perl with my favorite modules is pretty
    easy if you maintain a private bundle definition file. To get a useful
    blueprint of a bundle definition file, the command autobundle can be
    used on the CPAN shell command line. This command writes a bundle
    definition file for all modules that are installed for the currently
    running perl interpreter. It's recommended to run this command only once
    and from then on maintain the file manually under a private name, say
    Bundle/my_bundle.pm. With a clever bundle file you can then simply say

        cpan> install Bundle::my_bundle

    then answer a few questions and then go out for a coffee.

    Maintaining a bundle definition file means keeping track of two things:
    dependencies and interactivity. CPAN.pm sometimes fails on calculating
    dependencies because not all modules define all MakeMaker attributes
    correctly, so a bundle definition file should specify prerequisites as
    early as possible. On the other hand, it's a bit annoying that many
    distributions need some interactive configuring. So what I try to
    accomplish in my private bundle file is to have the packages that need
    to be configured early in the file and the gentle ones later, so I can
    go out after a few minutes and leave CPAN.pm untended.

WORKING WITH CPAN.pm BEHIND FIREWALLS
    Thanks to Graham Barr for contributing the following paragraphs about
    the interaction between perl, and various firewall configurations. For
    further information on firewalls, it is recommended to consult the
    documentation that comes with the ncftp program. If you are unable to go
    through the firewall with a simple Perl setup, it is very likely that
    you can configure ncftp so that it works for your firewall.

  Three basic types of firewalls
    Firewalls can be categorized into three basic types.

    http firewall
        This is where the firewall machine runs a web server and to access
        the outside world you must do it via the web server. If you set
        environment variables like http_proxy or ftp_proxy to a values
        beginning with http:// or in your web browser you have to set proxy
        information then you know you are running an http firewall.

        To access servers outside these types of firewalls with perl (even
        for ftp) you will need to use LWP.

    ftp firewall
        This where the firewall machine runs an ftp server. This kind of
        firewall will only let you access ftp servers outside the firewall.
        This is usually done by connecting to the firewall with ftp, then
        entering a username like "user@outside.host.com"

        To access servers outside these type of firewalls with perl you will
        need to use Net::FTP.

    One way visibility
        I say one way visibility as these firewalls try to make themselves
        look invisible to the users inside the firewall. An FTP data
        connection is normally created by sending the remote server your IP
        address and then listening for the connection. But the remote server
        will not be able to connect to you because of the firewall. So for
        these types of firewall FTP connections need to be done in a passive
        mode.

        There are two that I can think off.

        SOCKS
            If you are using a SOCKS firewall you will need to compile perl
            and link it with the SOCKS library, this is what is normally
            called a 'socksified' perl. With this executable you will be
            able to connect to servers outside the firewall as if it is not
            there.

        IP Masquerade
            This is the firewall implemented in the Linux kernel, it allows
            you to hide a complete network behind one IP address. With this
            firewall no special compiling is needed as you can access hosts
            directly.

            For accessing ftp servers behind such firewalls you usually need
            to set the environment variable "FTP_PASSIVE" or the config
            variable ftp_passive to a true value.

  Configuring lynx or ncftp for going through a firewall
    If you can go through your firewall with e.g. lynx, presumably with a
    command such as

        /usr/local/bin/lynx -pscott:tiger

    then you would configure CPAN.pm with the command

        o conf lynx "/usr/local/bin/lynx -pscott:tiger"

    That's all. Similarly for ncftp or ftp, you would configure something
    like

        o conf ncftp "/usr/bin/ncftp -f /home/scott/ncftplogin.cfg"

    Your mileage may vary...

FAQ
    1)  I installed a new version of module X but CPAN keeps saying, I have
        the old version installed

        Most probably you do have the old version installed. This can happen
        if a module installs itself into a different directory in the @INC
        path than it was previously installed. This is not really a CPAN.pm
        problem, you would have the same problem when installing the module
        manually. The easiest way to prevent this behaviour is to add the
        argument "UNINST=1" to the "make install" call, and that is why many
        people add this argument permanently by configuring

          o conf make_install_arg UNINST=1

    2)  So why is UNINST=1 not the default?

        Because there are people who have their precise expectations about
        who may install where in the @INC path and who uses which @INC
        array. In fine tuned environments "UNINST=1" can cause damage.

    3)  I want to clean up my mess, and install a new perl along with all
        modules I have. How do I go about it?

        Run the autobundle command for your old perl and optionally rename
        the resulting bundle file (e.g. Bundle/mybundle.pm), install the new
        perl with the Configure option prefix, e.g.

            ./Configure -Dprefix=/usr/local/perl-5.6.78.9

        Install the bundle file you produced in the first step with
        something like

            cpan> install Bundle::mybundle

        and you're done.

    4)  When I install bundles or multiple modules with one command there is
        too much output to keep track of.

        You may want to configure something like

          o conf make_arg "| tee -ai /root/.cpan/logs/make.out"
          o conf make_install_arg "| tee -ai /root/.cpan/logs/make_install.out"

        so that STDOUT is captured in a file for later inspection.

    5)  I am not root, how can I install a module in a personal directory?

        First of all, you will want to use your own configuration, not the
        one that your root user installed. If you do not have permission to
        write in the cpan directory that root has configured, you will be
        asked if you want to create your own config. Answering "yes" will
        bring you into CPAN's configuration stage, using the system config
        for all defaults except things that have to do with CPAN's work
        directory, saving your choices to your MyConfig.pm file.

        You can also manually initiate this process with the following
        command:

            % perl -MCPAN -e 'mkmyconfig'

        or by running

            mkmyconfig

        from the CPAN shell.

        You will most probably also want to configure something like this:

          o conf makepl_arg "LIB=~/myperl/lib \
                            INSTALLMAN1DIR=~/myperl/man/man1 \
                            INSTALLMAN3DIR=~/myperl/man/man3 \
                            INSTALLSCRIPT=~/myperl/bin \
                            INSTALLBIN=~/myperl/bin"

        and then (oh joy) the equivalent command for Module::Build. That
        would be

          o conf mbuildpl_arg "--lib=~/myperl/lib \
                            --installman1dir=~/myperl/man/man1 \
                            --installman3dir=~/myperl/man/man3 \
                            --installscript=~/myperl/bin \
                            --installbin=~/myperl/bin"

        You can make this setting permanent like all "o conf" settings with
        "o conf commit" or by setting "auto_commit" beforehand.

        You will have to add ~/myperl/man to the MANPATH environment
        variable and also tell your perl programs to look into ~/myperl/lib,
        e.g. by including

          use lib "$ENV{HOME}/myperl/lib";

        or setting the PERL5LIB environment variable.

        While we're speaking about $ENV{HOME}, it might be worth mentioning,
        that for Windows we use the File::HomeDir module that provides an
        equivalent to the concept of the home directory on Unix.

        Another thing you should bear in mind is that the UNINST parameter
        can be dangerous when you are installing into a private area because
        you might accidentally remove modules that other people depend on
        that are not using the private area.

    6)  How to get a package, unwrap it, and make a change before building
        it?

        Have a look at the "look" (!) command.

    7)  I installed a Bundle and had a couple of fails. When I retried,
        everything resolved nicely. Can this be fixed to work on first try?

        The reason for this is that CPAN does not know the dependencies of
        all modules when it starts out. To decide about the additional items
        to install, it just uses data found in the META.yml file or the
        generated Makefile. An undetected missing piece breaks the process.
        But it may well be that your Bundle installs some prerequisite later
        than some depending item and thus your second try is able to resolve
        everything. Please note, CPAN.pm does not know the dependency tree
        in advance and cannot sort the queue of things to install in a
        topologically correct order. It resolves perfectly well IF all
        modules declare the prerequisites correctly with the PREREQ_PM
        attribute to MakeMaker or the "requires" stanza of Module::Build.
        For bundles which fail and you need to install often, it is
        recommended to sort the Bundle definition file manually.

    8)  In our intranet we have many modules for internal use. How can I
        integrate these modules with CPAN.pm but without uploading the
        modules to CPAN?

        Have a look at the CPAN::Site module.

    9)  When I run CPAN's shell, I get an error message about things in my
        /etc/inputrc (or ~/.inputrc) file.

        These are readline issues and can only be fixed by studying readline
        configuration on your architecture and adjusting the referenced file
        accordingly. Please make a backup of the /etc/inputrc or ~/.inputrc
        and edit them. Quite often harmless changes like uppercasing or
        lowercasing some arguments solves the problem.

    10) Some authors have strange characters in their names.

        Internally CPAN.pm uses the UTF-8 charset. If your terminal is
        expecting ISO-8859-1 charset, a converter can be activated by
        setting term_is_latin to a true value in your config file. One way
        of doing so would be

            cpan> o conf term_is_latin 1

        If other charset support is needed, please file a bugreport against
        CPAN.pm at rt.cpan.org and describe your needs. Maybe we can extend
        the support or maybe UTF-8 terminals become widely available.

        Note: this config variable is deprecated and will be removed in a
        future version of CPAN.pm. It will be replaced with the conventions
        around the family of $LANG and $LC_* environment variables.

    11) When an install fails for some reason and then I correct the error
        condition and retry, CPAN.pm refuses to install the module, saying
        "Already tried without success".

        Use the force pragma like so

          force install Foo::Bar

        Or you can use

          look Foo::Bar

        and then 'make install' directly in the subshell.

    12) How do I install a "DEVELOPER RELEASE" of a module?

        By default, CPAN will install the latest non-developer release of a
        module. If you want to install a dev release, you have to specify
        the partial path starting with the author id to the tarball you wish
        to install, like so:

            cpan> install KWILLIAMS/Module-Build-0.27_07.tar.gz

        Note that you can use the "ls" command to get this path listed.

    13) How do I install a module and all its dependencies from the
        commandline, without being prompted for anything, despite my CPAN
        configuration (or lack thereof)?

        CPAN uses ExtUtils::MakeMaker's prompt() function to ask its
        questions, so if you set the PERL_MM_USE_DEFAULT environment
        variable, you shouldn't be asked any questions at all (assuming the
        modules you are installing are nice about obeying that variable as
        well):

            % PERL_MM_USE_DEFAULT=1 perl -MCPAN -e 'install My::Module'

    14) How do I create a Module::Build based Build.PL derived from an
        ExtUtils::MakeMaker focused Makefile.PL?

        http://search.cpan.org/search?query=Module::Build::Convert

        http://www.refcnt.org/papers/module-build-convert

    15) What's the best CPAN site for me?

        The urllist config parameter is yours. You can add and remove sites
        at will. You should find out which sites have the best uptodateness,
        bandwidth, reliability, etc. and are topologically close to you.
        Some people prefer fast downloads, others uptodateness, others
        reliability. You decide which to try in which order.

        Henk P. Penning maintains a site that collects data about CPAN
        sites:

          http://www.cs.uu.nl/people/henkp/mirmon/cpan.html

    16) Why do I get asked the same questions every time I start the shell?

        You can make your configuration changes permanent by calling the
        command "o conf commit". Alternatively set the "auto_commit"
        variable to true by running "o conf init auto_commit" and answering
        the following question with yes.

COMPATIBILITY
  OLD PERL VERSIONS
    CPAN.pm is regularly tested to run under 5.004, 5.005, and assorted
    newer versions. It is getting more and more difficult to get the minimal
    prerequisites working on older perls. It is close to impossible to get
    the whole Bundle::CPAN working there. If you're in the position to have
    only these old versions, be advised that CPAN is designed to work fine
    without the Bundle::CPAN installed.

    To get things going, note that GBARR/Scalar-List-Utils-1.18.tar.gz is
    compatible with ancient perls and that File::Temp is listed as a
    prerequisite but CPAN has reasonable workarounds if it is missing.

  CPANPLUS
    This module and its competitor, the CPANPLUS module, are both much
    cooler than the other. CPAN.pm is older. CPANPLUS was designed to be
    more modular but it was never tried to make it compatible with CPAN.pm.

SECURITY ADVICE
    This software enables you to upgrade software on your computer and so is
    inherently dangerous because the newly installed software may contain
    bugs and may alter the way your computer works or even make it unusable.
    Please consider backing up your data before every upgrade.

BUGS
    Please report bugs via <http://rt.cpan.org/>

    Before submitting a bug, please make sure that the traditional method of
    building a Perl module package from a shell by following the
    installation instructions of that package still works in your
    environment.

AUTHOR
    Andreas Koenig "<andk@cpan.org>"

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

    See <http://www.perl.com/perl/misc/Artistic.html>

TRANSLATIONS
    Kawai,Takanori provides a Japanese translation of this manpage at
    <http://homepage3.nifty.com/hippo2000/perltips/CPAN.htm>

SEE ALSO
    cpan, CPAN::Nox, CPAN::Version

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