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## File: $Id: README,v 1.2 2004/01/07 15:24:07 spadkins Exp $
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1. What is the App-Options distribution?

The App-Options distribution is "yet another command line processor."
However, it was created for maximum ease of use with the needs of
the Perl 5 Enterprise Environment in mind (more on that later).

The distribution consists of one Perl module and one shell script.

   App::Options - a perl module which combines command line parameters,
       environment variables, and configuration files to produce
       a hash of option values.

   prefix - a shell script which works for ksh (Korn shell) or
       bash (Bourne Again Shell) which allows you to change
       a family of environment variables (PATH, LD_LIBRARY_PATH,
       MANPATH, etc.) necessary for running programs out of a
       directory in which software has been installed.

2. What are the features?

FEATURES OF App::Options

 o Flexible command line syntax
   Parse long (--whatever) and short (-w) command line options
   (with [--verbose=3] or without [--verbose] arguments)
   and just put the values in %App::options (or some other hash
   that you may specify).
 o Automatic boolean command line switches
   An option like "--help" is equivalent to "--help=1".
 o Combines options with Environment Variables
   The --whatever=value option can be supplied with the
   APP_WHATEVER environment variable.
 o Combines options with variables in global and local config files
   The --whatever=value option can be supplied in config files with
   the "whatever = value" statement.  Initialization searches
   "$HOME/.app/$prog.conf", "$HOME/.app/app.conf",
   "$progdir/$prog.conf", "$progdir/app.conf",
   "$prefix/$prog.conf", and "$prefix/app.conf" in order
   to find the option values.
 o Import other files with "import = filename" statement
   Config files can, in essence, include other config files.
 o Stop importing other files with "flush_imports = 1" statement
   A config file can use this statement to tell the program
   to stop searching for other config files it was planning
   on searching.
 o Option values undergo variable expansion
   This means that some values may rely on other values.
   i.e. "prefix = /usr/mycompany/3.2.1" and "logdir = ${prefix}/log"
 o Config files can have conditional sections
   A section specifier "[cleanup]" begins a section only valid
   for the program "cleanup" (or "cleanup.exe" or cleanup.pl, etc.).
   A section specifier "[ALL]" (or just "[]") begins another
   unconditional section.  In fact, "[cleanup]" is just a synonym
   for "[app=cleanup]".  Sections can be made conditional on the
   current values of any variables. i.e. "[country=US;city=LAX]"
   would begin a section of variables only valid if the two
   specified variables have the required values.
 o Config files can have conditional lines
   Any section specifier can apply only to a single line by
   putting a statement after it. "[city=LAX] state = CA"
 o Modify @INC variable with the "perlinc = path1,path2" statement
   If invoked in the BEGIN block, this allows the person deploying
   the software to set up the Perl include path so that a
   particular version of the software installed on the system is
   used.  Subsequent uses of "use" and "require" will load modules
   from the configured locations.
 o Validate that "required" options are provided
   Certain options can be identified as required. Otherwise the
   program will not run.
 o Validate option values against types
   Certain options can be identified as to their type or pattern
   (integer, int, float, number, date, datetime, string, regexp).
   If the option value is provided and it does not match the
   type or pattern, the program will not run.
 o Provide automatic "-?" and "--help" messages
   Adds user-friendliness to programs with no extra effort.

3. What were the design goals that make this distribution unique?

 #1 Support multiple installations of a complex suite of software.
    This is useful for development and deployment of large systems,
    where multiple versions may be in varying states of development,
    testing, or production.

 #2 Support a suite of programs all using a common set of configuration
    files.  Large systems have many programs.  We don't want to 
    repeat the database name, username, and password in a separate
    config file for each program.

 #3 Make it so easy to use that a developer would be silly not to
    use it in even his smallest and simplest of scripts.  However,
    it should be powerful enough to support advanced features as
    the developer needs them.

 #4 Support conditions where the environment variables are not
    easy to control. i.e. CGI programs or cron jobs.

These were important design goals to support the App-Context variant
of the Perl 5 Enterprise Environment (P5EE).  See the P5EE website
(http://www.officevision.com/pub/p5ee) for more details.

4. Why another module? Why not use Getopt::Long or others?

There are many configuration modules on CPAN.  See

 http://search.cpan.org/modlist/Option_Parameter_Config_Processing

The most important feature was to be able to run it within a
BEGIN block to modify the Perl include path (@INC).  This is
most of design goal #1.  This means very few dependencies and
only on core modules.

I started by writing a few lines of code in a BEGIN block.
Then it got to be a lot of lines of code in a BEGIN block.
Then I moved it out to a module so I could reuse it easily.
Then it grew into a full-fledged command line, environment
variable, and config file value option processor.

In retrospect, I don't really know whether or not the other
modules can run just as well in a BEGIN block and have a special
feature to modify @INC.  However, this met a primary design
goal of App::Options.

I did try Getopt::Long, but it wasn't that easy to use, you had
to code your own "--help" feature, and it didn't incorporate
environment variables or config files.  I wanted something
more high-level and full-featured, so I wrote App::Options.

I looked at the description of the AppConfig distribution,
and it sounds similar to what I describe here.  However,
the meaning of "sections" (i.e. "[cleanup]") is a conditional
construct in App::Options.  Thus, it supports a single
family of configuration files to configure a whole suite
of programs and scripts. (Each program can have its own
section, and optionally its own file in both "user" and
"system" places.)  This met design goal #2.

See the section below on ease of use for design goal #3.

Design goal #4 required the autodetection of the ${prefix}
variable.  Thus, the App::Options module is integrated with
the discipline of choosing a root directory for your
software installation (i.e. PREFIX=/usr/mycompany/2.0.12).

5. You say it's so easy. Show me.

  #!/usr/bin/perl

  BEGIN {
      use App::Options;
      App::Options->init();
  }

  # now use the %App::options hash
  print "yada yada\n" if ($App::options{verbose});

It's that easy.

And it automatically has "-?" and "--help" support without
you having to code a thing.

Read the man page (or the code) if you want more power.

6. How do I install it?

To install this module, cd to the directory that contains this README
file and type the following (as usual).

   perl Makefile.PL
   make
   make test
   make install

