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 => $file);
ABSTRACT
"Config::Scoped" is a configuration file parser.
Features
* recursive data structures with scalars, lists, and hashes
* parses ISC named and dhcpd config files
* parses many Perl data structures without "eval", "do" or "require"
* Perl quoting syntax: single quotes (''), double quotes(""), and here
docs ("<<EOF")
* Perl code evaluation in "Safe" compartments
* simplified syntax with minimal punctuation
* include files with recursion checks
* controlled macro expansion in double quoted tokens
* lexically scoped parameter assignments and directives
* duplicate macro, parameter, and declaration checks
* file permission and ownership safety checks
* fine control over error checking
* error messages report config file names and line numbers
* exception-based error handling
* "Parse::RecDescent"-based parser; precompiled grammar for speed
* configuration caching with MD5 checksums on the original files
* may be subclassed to build parsers with specialized features
REQUIRES
* "Parse::RecDescent"
* "Error"
EXPORTS
Nothing.
METHODS
*$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.