# Main-2.6.0

**URL:** <https://www.ruby-forum.com/t/main-2-6-0/122331>\
**Category:** Ruby\
**Created:** [December 6, 2007, 5:52pm UTC](https://www.ruby-forum.com/t/main-2-6-0/122331 "2007-12-06T17:52:21Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![ara.t.howard](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/a8b319/32.png) [@ara.t.howard](https://www.ruby-forum.com/u/ara.t.howard)\
**Post date:** [December 6, 2007, 5:52pm UTC](https://www.ruby-forum.com/t/main-2-6-0/122331/1 "2007-12-06T17:52:21Z")

</div>

NAME  
main.rb

SYNOPSIS  
a class factory and dsl for generating command line programs real  
quick

URI  
[http://codeforpeople.com/lib/ruby/](http://codeforpeople.com/lib/ruby/)  
[http://rubyforge.org/projects/codeforpeople/](http://rubyforge.org/projects/codeforpeople/)  
[http://codeforpeople.rubyforge.org/svn/](http://codeforpeople.rubyforge.org/svn/)

INSTALL  
gem install main

HISTORY  
2.6.0  
- added ‘mixin’ feaature for storing, and later evaluating a  
block of  
code. the purpose of this is for use with modes where you  
want to keep  
your code dry, but may not want to define something in the  
base class  
for all to inherit. ‘mixin’ allows you to define the code to  
inherit  
once and the selectively drop it in child classes (modes) on  
demand.  
for example

```
     Main {
       mixin :foobar do
         option 'foo'
         option 'bar'
       end

       mode :install do
         mixin :foobar
       end

       mode :uninstall do
         mixin :foobar
       end

       mode :clean do
       end
     }

 - mode definitions are now deferred to the end of the Main

```

block, so you  
can do this

```
     Main {
       mode 'a' do
         mixin :foo
       end

       mode 'b' do
         mixin :foo
       end

       def inherited_method
         42
       end

       mixin 'foo' do
         def another_inherited_method
           'forty-two'
         end
       end
     }

 - added sanity check at end of paramter contruction

 - improved auto usage generation when arity is used with arguments

 - removed 'p' shortcut in paramerter dsl because it collided with
   Kernel.p. it's now called 'param'. this method is availble

```

_inside_ a  
parameter definition

```
     option('foo', 'f'){
       synopsis "arity = #{ param.arity }"
     }

 - fixed bug where '--' did not signal the end of parameter

```

parsing in a  
getoptlong compliant way

```
 - added (before/after)_parse_parameters, (before/after)

```

\_initialize, and  
(before/after)\_run hooks

```
 - fixed bug where adding to usage via

     usage['my_section'] = 'custom message'

   totally horked the default auto generated usage message

 - updated dependancies in gemspec.rb for attributes (~> 5.0.0) and
   arrayfields (~> 4.3.0)

 - check that client code defined run, iff not wrap_run! is

```

called. this is  
so mains with a mode, but no run defined, still function  
correctly when  
passed a mode

```
 - added new shortcut for creating accessors for parameters. for

```

example

```
     option('foo'){
       argument :required
       cast :int
       attr
     }

     def run
       p foo ### this attr will return the parameter's *value*
     end

   a block can be passed to specify how to extract the value from

```

the  
parameter

```
     argument('foo'){
       optional
       default 21
       cast :int
       attr{|param| param.value * 2}
     }

     def run
       p foo #=> 42
     end

 - fixed bug where 'abort("message")' would print "message" twice

```

on exit  
if running under a nested mode (yes again - the fix in 2.4.0  
wasn’t  
complete)

```
 - added a time cast, which uses Time.parse

     argument('login_time'){ cast :time }

 - added a date cast, which uses Date.parse

     argument('login_date'){ cast :date }

```

DESCRIPTION  
main.rb features the following:

```
 - unification of option, argument, keyword, and environment

```

parameter  
parsing  
- auto generation of usage and help messages  
- support for mode/sub-commands  
- io redirection support  
- logging hooks using ruby’s built-in logging mechanism  
- intelligent error handling and exit codes  
- use as dsl or library for building Main objects  
- parsing user defined ARGV and ENV  
- zero requirements for understanding the obtuse apis of _any_  
command  
line option parsers  
- leather pants

in short main.rb aims to drastically lower the barrier to writing  
uniform  
command line applications.

for instance, this program

```
 require 'main'

 Main {
   argument 'foo'
   option 'bar'

   def run
     p params['foo']
     p params['bar']
     exit_success!
   end
 }

```

sets up a program which requires one argument, ‘bar’, and which  
may accept one  
command line switch, ‘–foo’ in addition to the single option/mode  
which is always  
accepted and handled appropriately: ‘help’, ‘–help’, ‘-h’. for  
the most  
part main.rb stays out of your command line namespace but insists  
that your  
application has at least a help mode/option.

main.rb supports sub-commands in a very simple way

```
 require 'main'

 Main {
   mode 'install' do
     def run() puts 'installing...' end
   end

   mode 'uninstall' do
     def run() puts 'uninstalling...' end
   end
 }

```

which allows a program, called ‘a.rb’, to be invoked as

```
 ruby a.rb install

```

and

```
 ruby a.rb uninstall

```

for simple programs main.rb is a real time saver but it’s for more  
complex  
applications where main.rb’s unification of parameter parsing, class  
configuration dsl, and auto-generation of usage messages can  
really streamline  
command line application development. for example the following  
‘a.rb’  
program:

```
 require 'main'

 Main {
   argument('foo'){
     cast :int
   }
   keyword('bar'){
     arity 2
     cast :float
     defaults 0.0, 1.0
   }
   option('foobar'){
     argument :optional
     description 'the foobar option is very handy'
   }
   environment('BARFOO'){
     cast :list_of_bool
     synopsis 'export barfoo=value'
   }

   def run
     p params['foo'].value
     p params['bar'].values
     p params['foobar'].value
     p params['BARFOO'].value
   end
 }

```

when run with a command line of

```
 BARFOO=true,false,false ruby a.rb 42 bar=40 bar=2 --foobar=a

```

will produce

```
 42
 [40.0, 2.0]
 "a"
 [true, false, false]

```

while a command line of

```
 ruby a.rb --help

```

will produce

```
 NAME
   a.rb

 SYNOPSIS
   a.rb foo [bar=bar] [options]+

 PARAMETERS
   * foo [1 -> int(foo)]

   * bar=bar [2 ~> float(bar=0.0,1.0)]

   * --foobar=[foobar] [1 ~> foobar]
       the foobar option is very handy

   * --help, -h

   * export barfoo=value

```

and this shows how all of argument, keyword, option, and  
environment parsing  
can be declartively dealt with in a unified fashion - the dsl for all  
parameter types is the same - and how auto synopsis and usage  
generation saves  
keystrokes. the parameter synopsis is compact and can be read as

```
   * foo [1 -> int(foo)]

     'one argument will get processed via int(argument_name)'

       1 : one argument
       -> : will get processed (the argument is required)
       int(foo) : the cast is int, the arg name is foo

   * bar=bar [2 ~> float(bar=0.0,1.0)]

     'two keyword arguments might be processed via float

```

(bar=0.0,1.0)’

```
       2 : two arguments
       ~> : might be processed (the argument is

```

optional)  
float(bar=0.0,1.0) : the cast will be float, the default  
values are  
0.0 and 1.0

```
   * --foobar=[foobar] [1 ~> foobar]

     'one option with optional argument may be given directly'

   * --help, -h

     no synopsis, simple switch takes no args and is not required

   * export barfoo=value

     a user defined synopsis

```

SAMPLES

\<========\< samples/a.rb \>========\>

~ \> cat samples/a.rb

```
 require 'main'

 ARGV.replace %w( 42 ) if ARGV.empty?

 Main {
   argument('foo'){
     required # this is the default
     cast :int # value cast to Fixnum
     validate{|foo| foo == 42} # raises error in failure case
     description 'the foo param' # shown in --help
   }

   def run
     p params['foo'].given?
     p params['foo'].value
   end
 }

```

~ \> ruby samples/a.rb

```
 true
 42

```

~ \> ruby samples/a.rb --help

```
 NAME
   a.rb

 SYNOPSIS
   a.rb foo [options]+

 PARAMETERS
   foo (1 -> int(foo))
       the foo param
   --help, -h

```

\<========\< samples/b.rb \>========\>

~ \> cat samples/b.rb

```
 require 'main'

 ARGV.replace %w( 40 1 1 ) if ARGV.empty?

 Main {
   argument('foo'){
     arity 3 # foo will given three

```

times  
cast :int # value cast to Fixnum  
validate{|foo| [40,1].include? foo} # raises error in  
failure case  
description ‘the foo param’ # shown in --help  
}

```
   def run
     p params['foo'].given?
     p params['foo'].values
   end
 }

```

~ \> ruby samples/b.rb

```
 true
 [40, 1, 1]

```

~ \> ruby samples/b.rb --help

```
 NAME
   b.rb

 SYNOPSIS
   b.rb foo foo foo [options]+

 PARAMETERS
   foo (3 -> int(foo))
       the foo param
   --help, -h

```

\<========\< samples/c.rb \>========\>

~ \> cat samples/c.rb

```
 require 'main'

 ARGV.replace %w( foo=40 foo=2 bar=false ) if ARGV.empty?

 Main {
   keyword('foo'){
     required # by default keywords are not required
     arity 2
     cast :float
   }
   keyword('bar'){
     cast :bool
   }

   def run
     p params['foo'].given?
     p params['foo'].values
     p params['bar'].given?
     p params['bar'].value
   end
 }

```

~ \> ruby samples/c.rb

```
 true
 [40.0, 2.0]
 true
 false

```

~ \> ruby samples/c.rb --help

```
 NAME
   c.rb

 SYNOPSIS
   c.rb foo=foo [bar=bar] [options]+

 PARAMETERS
   foo=foo (2 -> float(foo))
   bar=bar (1 ~> bool(bar))
   --help, -h

```

\<========\< samples/d.rb \>========\>

~ \> cat samples/d.rb

```
 require 'main'

 ARGV.replace %w( --foo=40 -f2 ) if ARGV.empty?

 Main {
   option('foo', 'f'){
     required # by default options are not required, we could

```

use ‘foo=foo’  
# above as a shortcut  
argument\_required  
arity 2  
cast :float  
}

```
   option('bar=[bar]', 'b'){ # note shortcut syntax for optional

```

args  
# argument\_optional # we could also use this method  
cast :bool  
default false  
}

```
   def run
     p params['foo'].given?
     p params['foo'].values
     p params['bar'].given?
     p params['bar'].value
   end
 }

```

~ \> ruby samples/d.rb

```
 true
 [40.0, 2.0]
 nil
 false

```

~ \> ruby samples/d.rb --help

```
 NAME
   d.rb

 SYNOPSIS
   d.rb --foo=foo [options]+

 PARAMETERS
   --foo=foo, -f (2 -> float(foo))
   --bar=[bar], -b (0 ~> bool(bar=false))
   --help, -h

```

DOCS  
test/main.rb

find ./lib |xargs vim -o

API

Main {

########################################################################

### 

# CLASS LEVEL

API #

########################################################################

### 

# 

# the name of the program, auto-set and used in usage

# 

```
 program 'foo.rb'

```

# 

# a short description of program functionality, auto-set and used

in usage

# 

```
 synopsis "foo.rb arg [options]+"

```

# 

# long description of program functionality, used in usage iff set

# 

```
 description <<-hdoc
   this text will automatically be indented to the right level.

   it should describe how the program works in detail
 hdoc

```

# 

# used in usage iff set

# 

```
 author 'removed_email_address@domain.invalid'

```

# 

# used in usage

# 

```
 version '0.0.42'

```

# 

# stdin/out/err can be anthing which responds to read/write or a

string

# which will be opened as in the appropriate mode

# 

```
 stdin '/dev/null'
 stdout '/dev/null'
 stderr open('/dev/null', 'w')

```

# 

# the logger should be a Logger object, something ‘write’-able, or

a string

# which will be used to open the logger. the logger\_level

specifies the

# initalize verbosity setting, the default is Logger::INFO

# 

```
 logger(( program + '.log' ))
 logger_level Logger::DEBUG

```

# 

# you can configure exit codes. the defaults are shown

# 

```
 exit_success # 0
 exit_failure # 1
 exit_warn # 42

```

# 

# the usage object is rather complex. by default it’s an object

which can

# be built up in sections using the

# 

# usage[“BUGS”] = "something about bugs’

# 

# syntax to append sections onto the already pre-built usage

message which

# contains program, synopsis, parameter descriptions and the like

# 

# however, you always replace the usage object wholesale with one

of your

# chosing like so

# 

```
 usage <<-txt
   my own usage message
 txt

```

########################################################################

### 

# MODE

API #

########################################################################

### 

# 

# modes are class factories that inherit from their parent class.

they can

# be nested _arbitrarily_ deep. usage messages are tailored for

each mode.

# modes are, for the most part, independant classes but parameters

are

# always a superset of the parent class - a mode accepts all of

it’s parents

# paramters _plus_ and additional ones

# 

```
 option 'inherited-option'
 argument 'inherited-argument'

 mode 'install' do
   option 'force' do
     description 'clobber existing installation'
   end

   def run
     inherited_method()
     puts 'installing...'
   end

   mode 'docs' do
     description 'installs the docs'

     def run
       puts 'installing docs...'
     end
   end
 end

 mode 'un-install' do
   option 'force' do
     description 'remove even if dependancies exist'
   end

   def run
     inherited_method()
     puts 'un-installing...'
   end
 end

 def run
   puts 'no mode yo?'
 end

 def inherited_method
   puts 'superclass_method...'
 end

```

########################################################################

### 

# PARAMETER

API #

########################################################################

### 

# 

# all the parameter types of argument|keyword|option|environment

share this

# api. you must specify the type when the parameter method is used.

# alternatively used one of the shortcut methods

# argument|keyword|option|environment. in otherwords

# 

# parameter(‘foo’){ type :option }

# 

# is synonymous with

# 

# option(‘foo’){ }

# 

```
 option 'foo' {
 #
 # required - whether this paramter must by supplied on the

```

command line.  
# note that you can create ‘required’ options with this keyword  
#  
required # or required true  
#  
# argument\_required - applies only to options.  
#  
argument\_required # argument :required  
#  
# argument\_optional - applies only to options.  
#  
argument\_optional # argument :optional  
#  
# cast - should be either a lambda taking one argument, or a symbol  
# designation one of the built in casts defined in Main::Cast.  
supported  
# types are :boolean|:integer|:float|:numeric|:string|:uri.  
built-in  
# casts can be abbreviated  
#  
cast :int  
#  
# validate - should be a lambda taking one argument and returning  
# true|false  
#  
validate{|int| int == 42}  
#  
# synopsis - should be a concise characterization of the  
paramter. a  
# default synopsis is built automatically from the parameter. this  
# information is displayed in the usage message  
#  
synopsis ‘–foo’  
#  
# description - a longer description of the paramter. it  
appears in the  
# usage also.  
#  
description ‘a long description of foo’  
#  
# arity - indicates how many times the parameter should appear  
on the  
# command line. the default is one. negative arities are  
supported and  
# follow the same rules as ruby methods/procs.  
#  
arity 2  
#  
# default - you can provide a default value in case none is  
given. the  
# alias ‘defaults’ reads a bit nicer when you are giving a list of  
# defaults for paramters of \> 1 arity  
#  
defaults 40, 2  
#  
# you can add custom per-parameter error handlers using the  
following  
#  
error :before do  
puts ‘this fires _before_ normal error handling using  
#instance\_eval…’  
end

```
   error do
     puts 'this fires *instead of* normal error handling using

```

#instance\_eval…’  
end

```
   error :after do
     puts 'this fires *after* normal error handling using

```

#instance\_eval…’  
end  
}

########################################################################

### 

# INSTANCE LEVEL

API #

########################################################################

### 

# 

# you must define a run method. it is the only method you must

define.

# 

```
 def run
   #
   # all parameters are available in the 'params' hash and via

```

the alias  
# ‘param’. it can be indexed via string or symbol. the  
values are all  
# Main::Parameter objects  
#  
foo = params[‘foo’]  
#  
# the given? method indicates whether or not the parameter was  
given on  
# the commandline/environment, etc. in particular this will  
not be true  
# when a default value was specified but no parameter was given  
#  
foo.given?  
#  
# the list of all values can be retrieved via ‘values’. note  
that this  
# is always an array.  
#  
p foo.values  
#  
# the **first** value can be retrieved via ‘value’. note that  
this  
# never an array.  
#  
p foo.value  
#  
# the methods debug|info|warn|error|fatal are delegated to the  
logger  
# object  
#  
info{ “this goes to the log” }  
#  
# you can set the exit\_status at anytime. this status is used  
when  
# exiting the program. exceptions cause this to be  
ext\_failure if, and  
# only if, the current value was exit\_success. in otherwords an  
# un-caught exception always results in a failing exit\_status  
#  
exit\_status exit\_failure  
#  
# a few shortcuts both set the exit\_status and exit the program.  
#  
exit\_success!  
exit\_failure!  
exit\_warn!  
end

}

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