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

SYNOPSIS
    Interactive mode:

      perl -MCPAN -e shell;

    Batch mode:

      use CPAN;

      autobundle, clean, install, make, recompile, test

DESCRIPTION
    The CPAN module is designed to automate the make and install of perl
    modules and extensions. It includes some searching capabilities and
    knows how to use Net::FTP or LWP (or lynx or an external ftp client) to
    fetch the raw data from the net.

    Modules 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. There is no
    status retained between sessions. 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.

    For extended searching capabilities there's a plugin for CPAN available,
    the CPAN::WAIT manpage. `CPAN::WAIT' is a full-text search engine that
    indexes all documents available in CPAN authors directories. If
    `CPAN::WAIT' is installed on your system, the interactive shell of
    <CPAN.pm> will enable the `wq', `wr', `wd', `wl', and `wh' commands
    which send queries to the WAIT server that has been configured for your
    installation.

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

  Interactive Mode

    The interactive mode is entered by running

        perl -MCPAN -e shell

    which puts you into a readline interface. You will have the most fun if
    you install Term::ReadKey and Term::ReadLine to enjoy both history and
    command completion.

    Once you are on the command line, type 'h' and the rest should be
    self-explanatory.

    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>.

    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 Makefile.PL (this behavior is controlled by
      *prerequisites_policy*.)

      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. The `force' command takes as a first argument the
      method to invoke (currently: `make', `test', or `install') and
      executes the command from scratch.

      Example:

          cpan> install OpenGL
          OpenGL is up to date.
          cpan> force install OpenGL
          Running make
          OpenGL-0.4/
          OpenGL-0.4/COPYRIGHT
          [...]

      A `clean' command results in a

        make clean

      being executed within the distribution file's working directory.

    get, readme, look module or distribution
      `get' downloads a distribution file without further action. `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.

    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' 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.

  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.

  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 visible
    version number), so the really hottest and newest distribution file 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.

  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(...)').

    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.

    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 MD5 Data::Dumper)){
              my $obj = CPAN::Shell->expand('Module',$mod);
              $obj->install;
          }

          # 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 if 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 suites 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 four Classes

  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 an
    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.

  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 (well, we try to handle a bit more, but without much
      enthusiasm).

  Debugging

    The debugging of this module is pretty difficult, 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.

    In interactive mode you can try "o debug" which will list options for
    debugging the various parts of the package. The output may not be very
    useful for you as it's just a by-product of my own testing, but if you
    have an idea which part of the package may have a bug, it's sometimes
    worth to give it a try and send me more specific output. You should know
    that "o debug" has built-in completion support.

  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.

CONFIGURATION
    When the CPAN module is installed, a site wide configuration file is
    created as CPAN/Config.pm. The default values defined there can be
    overridden in another configuration file: CPAN/MyConfig.pm. You can
    store this file in $HOME/.cpan/CPAN/MyConfig.pm if you want, because
    $HOME/.cpan is added to the search path of the CPAN module before the
    use() or require() statements.

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

      build_cache        size of cache for directories to build modules
      build_dir          locally accessible directory to build modules
      index_expire       after this many days refetch index files
      cpan_home          local directory reserved for this package
      dontload_hash      anonymous hash: modules in the keys will not be
                         loaded by the CPAN::has_inst() routine
      gzip               location of external program gzip
      inactivity_timeout breaks interactive Makefile.PLs after this
                         many seconds inactivity. Set to 0 to never break.
      inhibit_startup_message
                         if true, does not print the startup message
      keep_source_where  directory in which to keep the source (if we do)
      make               location of external make program
      make_arg           arguments that should always be passed to 'make'
      make_install_arg   same as make_arg for 'make install'
      makepl_arg         arguments passed to 'perl Makefile.PL'
      pager              location of external program more (or any pager)
      prerequisites_policy
                         what to do if you are missing module prerequisites
                         ('follow' automatically, 'ask' me, or 'ignore')
      scan_cache         controls scanning of cache ('atstart' or 'never')
      tar                location of external program tar
      unzip              location of external program unzip
      urllist            arrayref to nearby CPAN sites (or equivalent locations)
      wait_list          arrayref to a wait server to try (See CPAN::WAIT)
      ftp_proxy,      }  the three usual variables for configuring
        http_proxy,   }  proxy requests. Both as CPAN::Config variables
        no_proxy      }  and as environment variables configurable.

    You can set and query each of these options interactively in the cpan
    shell with the command set defined within the `o conf' command:

    `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.

  Note on urllist parameter's format

    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/

  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.

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.
    If somebody has managed to tamper with the distribution file, they may
    have as well tampered with the CHECKSUMS file. Future development will
    go towards strong authentication.

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
    oneliners.

POPULATE AN INSTALLATION WITH LOTS OF MODULES
    To populate a freshly installed perl with my favorite modules is pretty
    easiest by maintaining 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 to keep 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 unattained.

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 informations 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 a 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 a 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 themselve
        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 need as you can access hosts
            directly.

  Configuring lynx or ncftp for going throught the 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 milage may vary...

FAQ
    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

    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.

    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.

BUGS
    We should give coverage for all of the CPAN and not just the PAUSE part,
    right? In this discussion CPAN and PAUSE have become equal -- but they
    are not. PAUSE is authors/ and modules/. CPAN is PAUSE plus the clpa/,
    doc/, misc/, ports/, src/, scripts/.

    Future development should be directed towards a better integration of
    the other parts.

    If a Makefile.PL requires special customization of libraries, prompts
    the user for special input, etc. then you may find CPAN is not able to
    build the distribution. In that case, you should attempt the traditional
    method of building a Perl module package from a shell.

AUTHOR
    Andreas Koenig <andreas.koenig@anima.de>

SEE ALSO
    perl(1), CPAN::Nox(3)

