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README

NAME
    Config::Scoped - feature rich configuration file parser

SYNOPSIS
      use Config::Scoped;

      $compartment = new Safe 'YOUR_SHARE';

      $warnings = 'off';  # or 'on'

      $warnings = { declaration  => 'off',  # or 'on'
                    digests      => 'off',
                    macro        => 'off',
                    parameter    => 'off',
                    permissions  => 'off',
                    your_warning => 'off' };

      $parser = new Config::Scoped file     => $config_file,
                                   lc       => $lc,
                                   safe     => $compartment,
                                   warnings => $warnings,
                                   your_key => $your_value;

      $config = $parser->parse;
      $config = $parser->parse(text => $config_string);

      $parser->set_warnings(name   => $name,
                            switch => 'on');   # or 'off'

      $parser->warnings_on(name => $name) and ...

      $parser->store_cache;
      $parser->store_cache   (cache => $file);

      $parser->retrieve_cache;
      $parser->retrieve_cache(cache => $file);

ABSTRACT
    "Config::Scoped" is a configuration file parser.

  Features
    *   recursive data structures with scalars, lists, and hashes

    *   parses ISC named and dhcpd config files

    *   parses many Perl data structures without "eval", "do" or "require"

    *   Perl quoting syntax: single quotes (''), double quotes(""), and here
        docs ("<<EOF")

    *   Perl code evaluation in "Safe" compartments

    *   simplified syntax with minimal punctuation

    *   include files with recursion checks

    *   controlled macro expansion in double quoted tokens

    *   lexically scoped parameter assignments and directives

    *   duplicate macro, parameter, and declaration checks

    *   file permission and ownership safety checks

    *   fine control over error checking

    *   error messages report config file names and line numbers

    *   exception-based error handling

    *   "Parse::RecDescent"-based parser

    *   configuration caching with MD5 checksums on the original files

    *   may be subclassed to build parsers with specialized features

REQUIRES
    *   "Parse::RecDescent"

    *   "Error"

EXPORTS
    Nothing.

METHODS
    *$parser* = "new" "Config::Scoped" "file" => *$config_file*, "lc" =>
    *$lc*, "safe" => *$compartment*, "warnings" => *$warnings*, "your_key"
    => *$your_value* [, ...]
        Creates and returns a new "Config::Scoped" object. All parameters
        are optional.

        *$config_file* is the configuration file to parse. If *$config_file*
        is omitted, then a *$config_string* must be provided to the "parse"
        method (see below).

        If *$lc* is true, all declaration and parameter names will be
        converted to lower case.

        *$compartment* is a "Safe" compartment for evaluating Perl code
        blocks in the configuration file. Defaults to a "Safe" compartment
        with no extra shares and the ":default" operator tag.

        *$warnings* may be

        the literal string 'on' or 'off'
            to set all warnings on or off

        a hash reference as shown in the "SYNOPSIS"
            to set each warning as specified in the hash

        All warnings are on by default.

        Arbitrary key/value pairs may be passed to the constructor, and will
        be stored in the *$parser* object. This is useful primarily to
        subclasses.

    *$config* = *$parser*->"parse"
    *$config* = *$parser*->"parse"("text" => *$config_string*)
        Parses the configuration and returns a reference to the config hash.

        The first form parses the *$config_file* that was provided to the
        constructor. If *$config_file* was not provided to the constructor,
        this form "die"s.

        The second form parses the *$config_string*.

        This method should only be called once.

    *$parser*->"set_warnings"("name" => *$name*, "switch" => 'on')
    *$parser*->"set_warnings"("name" => *$name*, "switch" => 'off')
        Set warning *$name* on or off.

    *$on* = *$parser*->"warnings_on"(name => $name)
        Returns true if warning *$name* is on. This is useful primarily to
        subclasses.

    *$parser*->"store_cache"("cache" => $cache_file)
    *$parser*->"store_cache"
        Stores the config hash on disk for rapid retrieval. If
        *$config_file* was provided to the constructor, then the stored form
        includes checksums of *$config_file* and any included files.

        The first form writes to *$cache_file*.

        The second form writes to *$config_file*".dump". If *$config_file*
        was not provided to the constructor, the second form "die"s.

    *$config* = *$parser*->"retrieve_cache"("cache" => *$cache_file*)
    *$config* = *$parser*->"retrieve_cache"
        Retrieves the *$config* hash from a file that was created by
        "store_cache".

        The first form reads *$cache_file*.

        The second form reads *$config_file*".dump". If *$config_file* was
        not provided to the constructor, the second form "die"s.

        The stored file is subject to "digests" and "permissions" checks.

EXCEPTIONS
    All methods "die" on error.

    "Config::Scoped::Error" defines a hierarchy of classes that represent
    "Config::Scoped" errors. When a method detects an error, it creates an
    instance of the corresponding class and throws it. The error classes are
    all subclasses of "Config::Scoped::Error". See Config::Scoped::Error for
    the complete list.

    If the exception is not caught, the program terminates, and
    "Config::Scoped" prints the config file name and line number where the
    error was detected to "STDERR".

CONFIG FILE FORMAT
    "Config::Scoped" reads configuration files. If we have a config file

      % cat host.cfg
      host
      {
          name = cpan.org
          port = 22
      }
      %

    we can read it into Perl with code like

      $parser = new Config::Scoped file => host.cfg;
      $config = $parser->parse;

    The resulting $config is always a hash ref. We'll call this the *config
    hash*, and write

      $config = {
                  host => { name => 'cpan.org',
                            port => 22        }
                }

    to show its contents. Fundamentally, "Config::Scoped" is a way to
    specify the contents of the config hash.

  Config files and config strings
    As shown in the "SYNOPSIS", "Config::Scoped" can obtain a configuration
    from a *$config_file*, passed to the constructor, or from a
    *$config_string*, passed to the "parse" method. For simplicity, we'll
    talk about parsing configuration files, distinguishing configuration
    strings only when necessary.

  File layout
    Config files are free-form ascii text. Comments begin with "#", and
    extend to the end of the line.

  Declarations
    The top-level elements of a config file are called *declarations*. A
    declaration consists of a name, followed by a block

      foo
      {
      }

      bar
      {
      }

    The declaration names become keys in the config hash. The value of each
    key is another hash ref. The config shown above parses to

      $config = {
                  foo => { },
                  bar => { }
                }

    You can create additional levels in the config hash simply by listing
    successive declaration names before the block. This config

      dog hound
      {
      }

      dog beagle
      {
      }

      cat
      {
      }

    parses to

      $config = {
                  dog => { hound  => { },
                           beagle => { } },

                  cat => { }
                }

    Declarations may not be nested.

  Parameters
    The ultimate purpose of a configuration file is to provide data values
    for a program. These values are specified by *parameters*. Parameters
    have the form

      name = value

    and go inside declaration blocks. The

      name = value

    parameters in a spec file become

      $name => $value

    pairs inside the declaration hashes in Perl code. For example, this
    configuration

      dog
      {
          legs  = 4
          wings = 0
      }

      bird
      {
          legs  = 2
          wings = 2
      }

    parses to

      $config = {
                  dog  => { legs  => 4,
                            wings => 0 },

                  bird => { legs  => 2,
                            wings => 2 }
                }

    Parameter values can be scalars, lists or hashes. Scalar values may be
    numbers or strings

      shape = square
      sides = 4

    Lists values are enclosed in square brackets

      colors = [ red green blue ]
      primes = [ 2 3 5 7 11 13  ]

    Hash values are enclosed in curly brackets

      capitals = { England => London
                   France  => Paris  }

    A hash value is also called a *hash block*.

    Lists and hashes can be nested to arbitrary depth

      Europe
      {
        currency = euro

        cities   = { England => [ London Birmingham Liverpool ]
                     France  => [ Paris Canne Calais ]         }
      }

    parses to

      $config = {
                  Europe => {
                              currency => 'euro',

                              cities => { England => [ 'London', 'Birmingham', 'Liverpool' ],
                                          France  => [ 'Paris', 'Canne', 'Calais'          ] }
                            }
                }

    The "Config::Scoped" data syntax is similar to the Perl data syntax, and
    "Config::Scoped" will parse many Perl data structures. In general,
    "Config::Scoped" requires less punctuation that Perl. Note that
    "Config::Scoped" allows arrow ("=>") or equals ("=") between hash keys
    and values, but not comma (",")

      capitals = { England => London        # OK
                   France  =  Paris         # OK
                   Germany ,  Berlin        # error
                 }

   _GLOBAL
    If a config file contains no declarations at all

      name = cpan.org
      port = 22

    then any parameters will be placed in a "_GLOBAL" declaration in the
    config hash

      $config = {
                  _GLOBAL => { name = cpan.org
                               port = 22       }
                }

    This allows very simple config files with just parameters and no
    declarations.

  Blocks, scoping and inheritance
    Each declaration block in a config file creates a lexical scope.
    Parameters inside a declaration are scoped to that block.

    Parameters are inherited by all following declarations within their
    scope. If all your animals have four legs, you can save some typing by
    writing

      legs = 4
      cat {}
      dog {}

    which parses to

      $config = {
                  cat => { legs => 4 }
                  dog => { legs => 4 }
                }

    If some of your animals have two legs, you can create additional scopes
    with anonymous blocks to control inheritance

      {
          legs = 4
          cat {}
          dog {}
      }
      {
          legs = 2
          bird {}
      }

    parses to

      $config = {
                  cat  => { legs => 4 }
                  dog  => { legs => 4 }
                  bird => { legs => 2 }
                }

    Anonymous blocks may be nested.

    Each hash block also creates a scope. The hash does not inherit
    parameters from outside its own scope.

  Perl code evaluation
    If you can't express what you need within the "Config::Scoped" syntax,
    your escape hatch is

      eval { ... }

    This does a Perl "eval" on the block, and replaces the construct with
    the results of the "eval".

      start = eval { localtime }
      foo   = eval { warn 'foo,' if $debug; return 'bar' }

    The block is evaluated in scalar context. However, it may return a list
    or hash reference, and the underlying list or hash can become a
    parameter value. For example

      a
      {
        list = eval { [ 1 .. 3 ]                 }
        hash = eval { { a => 1, b => 2, c => 3 } }
      }

    parses to

      $config = {
                  a => { list => [ 1, 2, 3 ],
                         hash => { a => 1, b => 2, c => 3 }
                }

    The block is evaluated inside the parser's "Safe" compartment. Variables
    can be made available to the "eval" by sharing them with the
    compartment. To set the $debug variable in the example above, do

      $compartment = new Safe 'MY_SHARE';
      $MY_SHARE::debug = 1;
      $parser = new Config::Scoped file => 'config.txt',
                                   safe => $compartment;
      $config = $parser->parse;

    Only global variables can be shared with a compartment; lexical
    variables cannot.

    "perl_code" is a synonym for "eval".

  Tokens and quoting
    A *token* is a

    *   declaration name

    *   parameter name

    *   hash key

    *   scalar value

    *   macro name

    *   macro value

    *   include path

    *   warning name

    Any token may be quoted. Tokens that contain special characters must be
    quoted. The special characters are

      \s {} [] <> () ; , ' " = # %

    "Config::Scoped" uses the Perl quoting syntax.

    Tokens may be quoted with either single or double quotes

      a = 'New York'
      b = "New Jersey\n"

    Here-docs are supported

      a = <<EOT
      New York
      New Jersey
      EOT

    but generalized quotes ("q()", "qq()", etc.) are not. Text in here-docs
    is regarded as single-quoted if the delimiter is enclosed in single
    quotes, and double-quoted if the delimiter is enclosed in double quotes
    or unquoted.

    Double-quoted tokens are evaluated as Perl strings inside the parser's
    "Safe" compartment. They are subject to the usual Perl backslash and
    variable interpolation, as well as macro expansion. Variables to be
    interpolated are passed via the "Safe" compartment, as shown above in
    "Perl code evaluation". If you need a literal "$" or "@" in a
    double-quoted string, be sure to escape it with a backslash ("\") to
    suppress interpolation.

    An

      eval { ... }

    may appear anywhere that a token is expected. For example

      a
      {
          eval { 'b' . 'c' } = 1
      }

    parses to

      $config = { a => { bc => 1 } }

DIRECTIVES
    "Config::Scoped" has three directives: %macro, %warning, and %include.

  Macros
    "Config::Scoped" supports macros. A macro is defined with

      %macro name value

    Macros may be defined

    *   at file scope

    *   within anonymous blocks

    *   within declaration blocks

    *   within hash blocks

    Macros defined within blocks are lexically scoped to those blocks.

    Macro substitution occurs

    *   within any double-quoted text

    *   within the entirety of Perl "eval" blocks

    *   nowhere else

  Include files
    "Config::Scoped" supports include files. To include one config file
    within another, write

      %include path/to/file

    %include directives may appear

    *   at file scope

    *   within anonymous blocks

    *   nowhere else

    In particular, %include directives may not appear within declaration
    blocks or hash blocks.

    Parameters and macros in include files are imported to the current
    scope. You can control this scope with an anonymous block

      {
        %include dog.cfg
        dog { }  # sees imports from dog.cfg
      }
      bird { }   # does not see imports from dog.cfg

    Warnings are scoped to the included file and do not leak to the parent
    file.

    Pathnames are either

    *   absolute

    *   relative to the dirname of the current configuration file

    For example, this config

        # in configuration file /etc/myapp/global.cfg
        %include shared.cfg

    includes the file /etc/myapp/shared.cfg. When parsing a configuration
    string, the path is relative to the current working directory.

    Include files are not actually included as text. Rather, they are
    processed by a recursive call to "Config::Scoped". Subclass implementers
    may need to be aware of this.

  Warnings
    "Config::Scoped" can check for five problems with config files

    *   duplicate declaration names

    *   duplicate parameter definitions

    *   duplicate macro definitions

    *   insecure config file permissions

    *   invalid config cache digests

    The API refers to these as "warnings", but they are actually errors, and
    if they occur, the parse fails and throws an exception. For consistency
    with the API, we'll use the term "warning" in the POD.

    The five warnings are identified by five predefined *warning names*

    *   "declaration"

    *   "parameter"

    *   "macro"

    *   "permissions"

    *   "digests"

    The "permissions" check requires that the config file

    *   be owned by root or the real UID of the running process AND

    *   have no group or world write permissions

    These restrictions help prevent an attacker from subverting a program by
    altering its config files.

    The "store_cache" method computes MD5 checksums for the config file and
    all included files. These checksums are stored with the cached
    configuration. The "retrieve_cache" method recomputes the checksums of
    the files and compares them to the stored values. The "digests" check
    requires that the checksums agree. This helps prevent programs from
    relying on stale configuration caches.

    All warnings are enabled by default. Warnings can be disabled by passing
    the "warning" key to the constructor, as shown in the "SYNOPSIS", or
    with the "set_warnings" method.

    Warnings can also be controlled with the %warnings directive, which has
    the form

    %warnings [*name*] "off"|"on"

    A %warnings directive applies to the *name*d warning, or to all
    warnings, if *name* is omitted.

    %warnings directives allow warnings to be turned on and off as necessary
    throughout the config file. A %warnings directive may appear

    *   at file scope

    *   within anonymous blocks

    *   within declaration blocks

    *   within hash blocks

    Each %warnings directive is lexically scoped to its enclosing file or
    block.

    Example

      legs = 4
      cat  {}
      dog  {}
      bird
      {
          legs = 2
      }

    fails with a duplicate parameter warning, but

      legs = 4
      cat  {}
      dog  {}
      bird
      {
          %warnings parameter off;
          legs = 2
      }

    successfully parses to

      $config = {
                  cat  => { legs => 4 }
                  dog  => { legs => 4 }
                  bird => { legs => 2 }
                }

Best practices
    As with all things Perl, there's more than one way to write
    configuration files. Here are some suggestions for writing config files
    that are concise, readable, and maintainable.

  Perl data
    "Config::Scoped" accepts most Perl data syntax. This allows Perl data to
    pulled into config files largely unaltered

      foo
      {
         a = 1;
         b = [ 'red', 'green', 'blue' ];
         c = { x => 5,
               y => 6 };
      }

    However, "Config::Scoped" doesn't require as much punctuation as Perl,
    and config files written from scratch will be cleaner without it

      foo
      {
         a = 1
         b = [ red green blue ]
         c = { x => 5
               y => 6 }
      }

  Anonymous blocks
    Don't use anonymous blocks unless you need to restrict the scope of
    something. In particular, there is no need for a top-level anonymous
    block around the whole config file

      {             # unnecessary
          foo { }
      }

  Inheritance
    Parameters that are outside of a declaration are inherited by all
    following declarations in their scope. Don't do this unless you mean it

      wheels = 4
      car
      {
          # OK
      }
      cat
      {
          # I can haz weelz?
      }

  Blocks, blocks, we got blocks...
    "Config::Scoped" has four different kinds of blocks

    *   anonymous

    *   declaration

    *   "eval"

    *   hash

    They all look the same, but they aren't, and they have different rules
    and restrictions. See "CONFIG FILE FORMAT" for descriptions of each.

  Macros
    Macros are evil, and "Config::Scoped" macros are specially evil, because

    *   they don't respect token boundaries

    *   where multiple substitutions are possible, the substitution order is
        undefined

    *   substituted text may or may not be rescanned for further
        substitutions

    Caveat scriptor.

SUBCLASSING
    "Config::Scoped" has no formally defined subclass interface. Here are
    some guidelines for writing subclasses. Implementers who override (or
    redefine) base class methods may need to read the "Config::Scoped"
    sources for more information.

    Arbitrary

      $key => $value

    pairs may be passed to the "Config::Scoped" constructor. They will be
    stored in the *$parser* object, and methods may access them with code
    like

      $parser->{local}{$key}

    To avoid conflict with existing keys in the "local" hash, consider
    distinguishing your keys with a unique prefix.

    Arbitrary warning names may be defined, set with "new" and
    "set_warnings", used in %warnings directives, and tested with
    "warnings_on". Methods can call "warnings_on" to find out whether a
    warning is currently enabled.

    All methods throw exceptions ("die") on error. The exception object
    should be a subclass of "Config::Scoped::Error". You can use one of the
    classes defined in "Config::Scoped::Error", or you can derive your own.
    This code

      throw Config::Scoped::Error -file => $parser->_get_file(%args),
                                  -line => $parser->_get_line(%args),
                                  -text => $message;

    will generate an error message that reports the location in the config
    file where the error was detected, rather than a location in Perl code.

    "Config::Scoped" performs validation checks on the elements of
    configuration files (declarations, parameters, macros, etc). Here are
    the interfaces to the validation methods. Subclasses can override these
    methods to modify or extend the validation checks.

    *$macro_value* = *$parser*->"macro_validate"("name" => *$name*, "value"
    => *$value*)
        Called for each %macro directive.

        Receives the *$name* and *$value* from the directive. The returned
        *$macro_value* becomes the actual value of the macro.

        If the macro is invalid, throws a
        "Config::Scoped::Error::Validate::Macro" exception.

    *$param_value* = *$parser*->"parameter_validate"("name" => *$name*,
    "value" => *$value*)
        Called for each parameter definition.

        Receives the *$name* and *$value* from the definition. The returned
        *$param_value* becomes the actual value of the parameter.

        If the parameter is invalid, throws a
        "Config::Scoped::Error::Validate::Parameter" exception.

    *$parser*->"declaration_validate"("name" => *$name*, "value" =>
    *$value*, "tail" => *$tail*)
        Called for each declaration.

        *$name* is an array ref giving the chain of names for the
        declaration block. *$value* is a hash ref containing all the
        parameters in the declaration block. *$tail* is a hash ref
        containing all the parameters in any previously defined declaration
        with the same name(s).

        For example, the declaration

          foo bar baz { a=1 b=2 }

        leads to the call

          $parser->declaration_validate(name  => [ qw(foo bar baz) ],
                                        value => { a => '1', b => '2' },
                                        tail  => $parser->{local}{config}{foo}{bar}{baz});

        The method can test %$tail to discover if there is an existing,
        non-empty declaration with the same name(s).

        The method has no return value. However, the method can alter the
        contents of %$value. Upon return, the parameters in %$value become
        the actual contents of the declaration block.

        If the declaration is invalid, throws a
        "Config::Scoped::Error::Validate::Declaration" exception.

    *$parser*->"permissions_validate"(file => *$file*, handle => *$handle*)
        Called for the config file, each included file, and each retrieved
        cache file. One of *$file* or *$handle* will be non-null.

        Throws a "Config::Scoped::Error::Validate::Permissions" exception if
        the file is not safe to read.

SEE ALSO
    *   "Error"

    *   "Safe"

    *   "Config::Scoped::Error"

    *   "Parse::RecDescent"

    *   "Quote and Quote-like Operators" in perlop

TODO
    Tests
        Still more tests needed.

BUGS
    If you find parser bugs, please send the stripped down config file and
    additional version information to the author.

CREDITS
    POD by Steven W. McDougall <swmcd@world.std.com>

AUTHOR
    Karl Gaissmaier <karl.gaissmaier at uni-ulm.de>

COPYRIGHT AND LICENSE
    Copyright (c) 2004-2012 by Karl Gaissmaier

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

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