USING THE AppConfig MODULE¶

To import and use the AppConfig module the following line should appear in your Perl script:

     use AppConfig;

To import constants defined by the AppConfig module, specify the name of one or more of the constant or tag sets as parameters to "use":

    use AppConfig qw(:expand :argcount);

See "CONSTANT DEFINITIONS" below for more information on the constant tagsets defined by AppConfig.

AppConfig is implemented using object-oriented methods. A new AppConfig object is created and initialized using the new() method. This returns a reference to a new AppConfig object.

    my $config = AppConfig->new();

This will create and return a reference to a new AppConfig object.

In doing so, the AppConfig object also creates an internal reference to an AppConfig::State object in which to store variable state. All arguments passed into the AppConfig constructor are passed directly to the AppConfig::State constructor.

The first (optional) parameter may be a reference to a hash array containing configuration information.

    my $config = AppConfig->new( {
            CASE   => 1,
            ERROR  => \&my_error,
            GLOBAL => { 
                    DEFAULT  => "<unset>", 
                    ARGCOUNT => ARGCOUNT_ONE,
                },
        } );

See AppConfig::State for full details of the configuration options available. These are, in brief:

CASE

Used to set case sensitivity for variable names (default: off).

CREATE

Used to indicate that undefined variables should be created automatically (default: off).

GLOBAL

Reference to a hash array of global values used by default when defining variables. Valid global values are DEFAULT, ARGCOUNT, EXPAND, VALIDATE and ACTION.

PEDANTIC

Used to indicate that command line and configuration file parsing routines should return immediately on encountering an error.

ERROR

Used to provide a error handling routine. Arguments as per printf().

Subsequent parameters may be variable definitions. These are passed to the define() method, described below in "DEFINING VARIABLES".

    my $config = AppConfig->new("foo", "bar", "baz");
    my $config = AppConfig->new( { CASE => 1 }, qw(foo bar baz) );

Note that any unresolved method calls to AppConfig are automatically delegated to the AppConfig::State object. In practice, it means that it is possible to treat the AppConfig object as if it were an AppConfig::State object:

    # create AppConfig
    my $config = AppConfig->new('foo', 'bar');
    # methods get passed through to internal AppConfig::State
    $config->foo(100);
    $config->set('bar', 200);
    $config->define('baz');
    $config->baz(300);

DEFINING VARIABLES¶

The define() method (delegated to AppConfig::State) is used to pre-declare a variable and specify its configuration.

    $config->define("foo");

Variables may also be defined directly from the AppConfig new() constructor.

    my $config = AppConfig->new("foo");

In both simple examples above, a new variable called "foo" is defined. A reference to a hash array may also be passed to specify configuration information for the variable:

    $config->define("foo", {
            DEFAULT   => 99,
            ALIAS     => 'metavar1',
        });

Configuration items specified in the GLOBAL option to the module constructor are applied by default when variables are created. e.g.

    my $config = AppConfig->new( { 
        GLOBAL => {
            DEFAULT  => "<undef>",
            ARGCOUNT => ARGCOUNT_ONE,
        }
    } );
    $config->define("foo");
    $config->define("bar", { ARGCOUNT => ARGCOUNT_NONE } );

is equivalent to:

    my $config = AppConfig->new();
    $config->define( "foo", {
        DEFAULT  => "<undef>",
        ARGCOUNT => ARGCOUNT_ONE,
    } );
    $config->define( "bar", 
        DEFAULT  => "<undef>",
        ARGCOUNT => ARGCOUNT_NONE,
    } );

Multiple variables may be defined in the same call to define(). Configuration hashes for variables can be omitted.

    $config->define("foo", "bar" => { ALIAS = "boozer" }, "baz");

See AppConfig::State for full details of the configuration options available when defining variables. These are, in brief:

DEFAULT

The default value for the variable (default: undef).

ALIAS

One or more (list reference or "list|like|this") alternative names for the variable.

ARGCOUNT

Specifies the number and type of arguments that the variable expects. Constants in ":expand" tag set define ARGCOUNT_NONE - simple on/off flag (default), ARGCOUNT_ONE - single value, ARGCOUNT_LIST - multiple values accessed via list reference, ARGCOUNT_HASH - hash table, "key=value", accessed via hash reference.

ARGS

Used to provide an argument specification string to pass to Getopt::Long via AppConfig::Getopt. E.g. "=i", ":s", "=s@". This can also be used to implicitly set the ARGCOUNT value ("/^!/" = ARGCOUNT_NONE, "/@/" = ARGCOUNT_LIST, "/%/" = ARGCOUNT_HASH, "/[=:].*/" = ARGCOUNT_ONE)

EXPAND

Specifies which variable expansion policies should be used when parsing configuration files. Constants in ":expand" tag set define:

    EXPAND_NONE - no expansion (default) 
    EXPAND_VAR  - expand C<$var> or C<$(var)> as other variables
    EXPAND_UID  - expand C<~> and C<~uid> as user's home directory 
    EXPAND_ENV - expand C<${var}> as environment variable
    EXPAND_ALL - do all expansions.
    

VALIDATE

Regex which the intended variable value should match or code reference which returns 1 to indicate successful validation (variable may now be set).

ACTION

Code reference to be called whenever variable value changes.

COMPACT FORMAT DEFINITION¶

Variables can be specified using a compact format. This is identical to the specification format of Getopt::Long and is of the form:

    "name|alias|alias<argopts>"

The first element indicates the variable name and subsequent ALIAS values may be added, each separated by a vertical bar '|'.

The <argopts> element indicates the ARGCOUNT value and may be one of the following;

    !                  ARGCOUNT_NONE
    =s                 ARGCOUNT_ONE
    =s@                ARGCOUNT_LIST
    =s%                ARGCOUNT_HASH

Additional constructs supported by Getopt::Long may be specified instead of the "=s" element (e.g. "=f"). The entire <argopts> element is stored in the ARGS parameter for the variable and is passed intact to Getopt::Long when the getopt() method is called.

The following examples demonstrate use of the compact format, with their equivalent full specifications:

    $config->define("foo|bar|baz!");
    $config->define(
            "foo" => { 
                ALIAS    => "bar|baz", 
                ARGCOUNT => ARGCOUNT_NONE,
            });
    $config->define("name=s");
    $config->define(
            "name" => { 
                ARGCOUNT => ARGCOUNT_ONE,
            });
    $config->define("file|filelist|f=s@");
    $config->define(
            "file" => { 
                ALIAS    => "filelist|f", 
                ARGCOUNT => ARGCOUNT_LIST,
            });
    $config->define("user|u=s%");
    $config->define(
            "user" => { 
                ALIAS    => "u", 
                ARGCOUNT => ARGCOUNT_HASH,
            });

Additional configuration options may be specified by hash reference, as per normal. The compact definition format will override any configuration values provided for ARGS and ARGCOUNT.

    $config->define("file|filelist|f=s@", { VALIDATE => \&check_file } );

READING AND MODIFYING VARIABLE VALUES¶

AppConfig defines two methods (via AppConfig::State) to manipulate variable values

    set($variable, $value);
    get($variable);

Once defined, variables may be accessed directly as object methods where the method name is the same as the variable name. i.e.

    $config->set("verbose", 1);

is equivalent to

    $config->verbose(1);

Note that AppConfig defines the following methods:

    new();
    file();
    args();
    getopt();

And also, through delegation to AppConfig::State:

    define()
    get()
    set()
    varlist()

If you define a variable with one of the above names, you will not be able to access it directly as an object method. i.e.

    $config->file();

This will call the file() method, instead of returning the value of the 'file' variable. You can work around this by explicitly calling get() and set() on a variable whose name conflicts:

    $config->get('file');

or by defining a "safe" alias by which the variable can be accessed:

    $config->define("file", { ALIAS => "fileopt" });
or
    $config->define("file|fileopt");
    ...
    $config->fileopt();

Without parameters, the current value of the variable is returned. If a parameter is specified, the variable is set to that value and the result of the set() operation is returned.

    $config->age(29);        # sets 'age' to 29, returns 1 (ok)
    print $config->age();    # prints "29"

The varlist() method can be used to extract a number of variables into a hash array. The first parameter should be a regular expression used for matching against the variable names.

    my %vars = $config->varlist("^file");   # all "file*" variables

A second parameter may be specified (any true value) to indicate that the part of the variable name matching the regex should be removed when copied to the target hash.

    $config->file_name("/tmp/file");
    $config->file_path("/foo:/bar:/baz");
    my %vars = $config->varlist("^file_", 1);
    # %vars:
    #    name => /tmp/file
    #    path => "/foo:/bar:/baz"

READING CONFIGURATION FILES¶

The AppConfig module provides a streamlined interface for reading configuration files with the AppConfig::File module. The file() method automatically loads the AppConfig::File module and creates an object to process the configuration file or files. Variables stored in the internal AppConfig::State are automatically updated with values specified in the configuration file.

    $config->file($filename);

Multiple files may be passed to file() and should indicate the file name or be a reference to an open file handle or glob.

    $config->file($filename, $filehandle, \*STDIN, ...);

The file may contain blank lines and comments (prefixed by '#') which are ignored. Continutation lines may be marked by ending the line with a '\'.

    # this is a comment
    callsign = alpha bravo camel delta echo foxtrot golf hipowls \
               india juliet kilo llama mike november oscar papa  \
               quebec romeo sierra tango umbrella victor whiskey \
               x-ray yankee zebra

Variables that are simple flags and do not expect an argument (ARGCOUNT = ARGCOUNT_NONE) can be specified without any value. They will be set with the value 1, with any value explicitly specified (except "0" and "off") being ignored. The variable may also be specified with a "no" prefix to implicitly set the variable to 0.

    verbose                              # on  (1)
    verbose = 1                          # on  (1)
    verbose = 0                          # off (0)
    verbose off                          # off (0)
    verbose on                           # on  (1)
    verbose mumble                       # on  (1)
    noverbose                            # off (0)

Variables that expect an argument (ARGCOUNT = ARGCOUNT_ONE) will be set to whatever follows the variable name, up to the end of the current line (including any continuation lines). An optional equals sign may be inserted between the variable and value for clarity.

    room = /home/kitchen     
    room   /home/bedroom

Each subsequent re-definition of the variable value overwrites the previous value.

    print $config->room();               # prints "/home/bedroom"

Variables may be defined to accept multiple values (ARGCOUNT = ARGCOUNT_LIST). Each subsequent definition of the variable adds the value to the list of previously set values for the variable.

    drink = coffee
    drink = tea

A reference to a list of values is returned when the variable is requested.

    my $beverages = $config->drink();
    print join(", ", @$beverages);      # prints "coffee, tea"

Variables may also be defined as hash lists (ARGCOUNT = ARGCOUNT_HASH). Each subsequent definition creates a new key and value in the hash array.

    alias l="ls -CF"
    alias e="emacs"

A reference to the hash is returned when the variable is requested.

    my $aliases = $config->alias();
    foreach my $k (keys %$aliases) {
        print "$k => $aliases->{ $k }\n";
    }

The '-' prefix can be used to reset a variable to its default value and the '+' prefix can be used to set it to 1

    -verbose
    +debug

VARIABLE EXPANSION¶

Variable values may contain references to other AppConfig variables, environment variables and/or users' home directories. These will be expanded depending on the EXPAND value for each variable or the GLOBAL EXPAND value.

Three different expansion types may be applied:

    bin = ~/bin          # expand '~' to home dir if EXPAND_UID
    tmp = ~abw/tmp       # as above, but home dir for user 'abw'
    perl = $bin/perl     # expand value of 'bin' variable if EXPAND_VAR
    ripl = $(bin)/ripl   # as above with explicit parens
    home = ${HOME}       # expand HOME environment var if EXPAND_ENV

See AppConfig::State for more information on expanding variable values.

The configuration files may have variables arranged in blocks. A block header, consisting of the block name in square brackets, introduces a configuration block. The block name and an underscore are then prefixed to the names of all variables subsequently referenced in that block. The block continues until the next block definition or to the end of the current file.

    [block1]
    foo = 10             # block1_foo = 10
    [block2]
    foo = 20             # block2_foo = 20

PARSING COMMAND LINE OPTIONS¶

There are two methods for processing command line options. The first, args(), is a small and efficient implementation which offers basic functionality. The second, getopt(), offers a more powerful and complete facility by delegating the task to Johan Vroman's Getopt::Long module. The trade-off between args() and getopt() is essentially one of speed/size against flexibility. Use as appropriate. Both implement on-demand loading of modules and incur no overhead until used.

The args() method is used to parse simple command line options. It automatically loads the AppConfig::Args module and creates an object to process the command line arguments. Variables stored in the internal AppConfig::State are automatically updated with values specified in the arguments.

The method should be passed a reference to a list of arguments to parse. The @ARGV array is used if args() is called without parameters.

    $config->args(\@myargs);
    $config->args();               # uses @ARGV

Arguments are read and shifted from the array until the first is encountered that is not prefixed by '-' or '--'. At that point, the method returns 1 to indicate success, leaving any unprocessed arguments remaining in the list.

Each argument should be the name or alias of a variable prefixed by '-' or '--'. Arguments that are not prefixed as such (and are not an additional parameter to a previous argument) will cause a warning to be raised. If the PEDANTIC option is set, the method will return 0 immediately. With PEDANTIC unset (default), the method will continue to parse the rest of the arguments, returning 0 when done.

If the variable is a simple flag (ARGCOUNT = ARGCOUNT_NONE) then it is set to the value 1. The variable may be prefixed by "no" to set its value to 0.

    myprog -verbose --debug -notaste     # $config->verbose(1)
                                         # $config->debug(1)
                                         # $config->taste(0)

Variables that expect an additional argument (ARGCOUNT != 0) will be set to the value of the argument following it.

    myprog -f /tmp/myfile                # $config->file('/tmp/file');

Variables that expect multiple values (ARGCOUNT = ARGCOUNT_LIST or ARGCOUNT_HASH) will have successive values added each time the option is encountered.

    myprog -file /tmp/foo -file /tmp/bar # $config->file('/tmp/foo')
                                         # $config->file('/tmp/bar')
    # file => [ '/tmp/foo', '/tmp/bar' ]
    myprog -door "jim=Jim Morrison" -door "ray=Ray Manzarek"
                                    # $config->door("jim=Jim Morrison");
                                    # $config->door("ray=Ray Manzarek");
    # door => { 'jim' => 'Jim Morrison', 'ray' => 'Ray Manzarek' }

See AppConfig::Args for further details on parsing command line arguments.

The getopt() method provides a way to use the power and flexibility of the Getopt::Long module to parse command line arguments and have the internal values of the AppConfig object updates automatically.

The first (non-list reference) parameters may contain a number of configuration string to pass to Getopt::Long::Configure. A reference to a list of arguments may additionally be passed or @ARGV is used by default.

    $config->getopt();                       # uses @ARGV
    $config->getopt(\@myargs);
    $config->getopt(qw(auto_abbrev debug));  # uses @ARGV
    $config->getopt(qw(debug), \@myargs);

See Getopt::Long for details of the configuration options available.

The getopt() method constructs a specification string for each internal variable and then initializes Getopt::Long with these values. The specification string is constructed from the name, any aliases (delimited by a vertical bar '|') and the value of the ARGS parameter.

    $config->define("foo", {
        ARGS  => "=i",
        ALIAS => "bar|baz",
    });
    # Getopt::Long specification: "foo|bar|baz=i"

Errors and warning generated by the Getopt::Long module are trapped and handled by the AppConfig error handler. This may be a user-defined routine installed with the ERROR configuration option.

Please note that the AppConfig::Getopt interface is still experimental and may not be 100% operational. This is almost undoubtedly due to problems in AppConfig::Getopt rather than Getopt::Long.

PARSING CGI PARAMETERS¶

The cgi() method provides an interface to the AppConfig::CGI module for updating variable values based on the parameters appended to the URL for a CGI script. This is commonly known as the CGI "GET" method. The CGI "POST" method is currently not supported.

Parameter definitions are separated from the CGI script name by a question mark and from each other by ampersands. Where variables have specific values, these are appended to the variable with an equals sign:

    http://www.here.com/cgi-bin/myscript?foo=bar&baz=qux&verbose
        # $config->foo('bar');
        # $config->baz('qux');
        # $config->verbose(1);

Certain values specified in a URL must be escaped in the appropriate manner (see CGI specifications at http://www.w3c.org/ for full details). The AppConfig::CGI module automatically unescapes the CGI query string to restore the parameters to their intended values.

    http://where.com/mycgi?title=%22The+Wrong+Trousers%22
    # $config->title('"The Wrong Trousers"');

Please be considerate of the security implications of providing writable access to script variables via CGI.

    http://rebel.alliance.com/cgi-bin/...
        .../send_report?file=%2Fetc%2Fpasswd&email=darth%40empire.com

To avoid any accidental or malicious changing of "private" variables, define only the "public" variables before calling the cgi() (or any other) method. Further variables can subsequently be defined which can not be influenced by the CGI parameters.

    $config->define('verbose', 'debug')
    $config->cgi();             # can only set verbose and debug
    $config->define('email', 'file');
    $config->file($cfgfile);    # can set verbose, debug, email + file