A KISS pure Fortran Library for building powerful, easy-to-use, elegant command line interfaces

• FLAP is a pure Fortran (KISS) library for building easily nice Command Line Interfaces (CLI) for modern Fortran projects;
• FLAP is Fortran 2003+ standard compliant;
• FLAP is OOP designed;
• FLAP is a Free, Open Source Project.

• What is FLAP?
• Main features
• Copyrights
• Documentation
  • A Taste of FLAP

Modern Fortran standards (2003+) have introduced support for Command Line Arguments (CLA), thus it is possible to construct nice and effective Command Line Interfaces (CLI). FLAP is a small library designed to simplify the (repetitive) construction of complicated CLI in pure Fortran (standard 2003+). FLAP has been inspired by the python module argparse trying to mimic it. Once you have defined the arguments that are required by means of a user-friendly method of the CLI, FLAP will parse the CLAs for you. It is worthy of note that FLAP, as argparse, also automatically generates help and usage messages and issues errors when users give the program invalid arguments.

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FLAP is inspired by the python great module argparse, thus many features are taken from it. Here the main features are listed.

• User-friendly methods for building flexible and effective Command Line Interfaces (CLI);
• comprehensive Command Line Arguments (CLA) support:
  • support optional and non optional CLA;
  • support boolean CLA;
  • support positional CLA;
  • support list of allowable values for defined CLA with automatic consistency check;
  • support multiple valued (list of values) CLA;
  • self-consistency-check of CLA definition;
• automatic generation of help and usage messages;
• consistency-check of whole CLI definition;
• errors trapping for invalid CLI usage;
• support nested subcommands;
• support environment variables;
• POSIX style compliant;
• replicate all the useful features of argparse;
• implement docopt features.
• implement click features.

Any feature request is welcome.

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FLAP is an open source project, it is distributed under a dual licensing system: the GPL v3 and the MIT licenses. Anyone is interest to use, to develop or to contribute to FLAP is welcome: you are free to select the GPL license for FOSS projects or the MIT one for commercial softwares.

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Besides this README file the FLAP documentation is contained into its own wiki. Detailed documentation of the API is contained into the GitHub Pages that can also be created locally by means of ford tool.

Running the provided test program, Test_Driver -h, a taste of FLAP is served:

usage:  Test_Driver  [value] --string value [--integer value] [--real value] [--boolean] [--boolean_val value] [--integer_list value#1 value#2 value#3] [--help] [--version]

 Required options:
   --string value, -s value
       String input; required

 Optional options:
   value
       Positional real input; 1-th positional CLA; optional, default value 1.0
   --integer value, -i value, value in: (1,3,5)
       Integer input with fixed range; optional, default value 1
   --real value, -r value
       Real input; optional, default value 1.0
   --boolean, -b
       Boolean input; optional, default value .false.
   --boolean_val value, -bv value
       Valued boolean input; optional, default value .true.
   --integer_list value#1 value#2 value#3, -il value#1 value#2 value#3
       Integer list input; optional, default value 1 8 32
   --help, -h
       Print this help message; optional
   --version, -v
       Print version; optional

 Examples:
   -) Test_Driver -s 'Hello FLAP'
   -) Test_Driver -s 'Hello FLAP' -i -2 # printing error...
   -) Test_Driver -s 'Hello FLAP' -i 3 -r 33.d0
   -) Test_Driver -s 'Hello FLAP' --integer_list 10 -3 87
   -) Test_Driver 33.0 -s 'Hello FLAP' -i 5
   -) Test_Driver --string 'Hello FLAP' --boolean

Not so bad for just a very few statements as the following:

...
! initializing CLI
call cli%init(progname='Test_Driver',                                           &
              version ='v0.0.5',                                                &
              examples=["Test_Driver -s 'Hello FLAP'                          ",&
                        "Test_Driver -s 'Hello FLAP' -i -2 # printing error...",&
                        "Test_Driver -s 'Hello FLAP' -i 3 -r 33.d0            ",&
                        "Test_Driver -s 'Hello FLAP' --integer_list 10 -3 87  ",&
                        "Test_Driver 33.0 -s 'Hello FLAP' -i 5                ",&
                        "Test_Driver --string 'Hello FLAP' --boolean          "])
! setting CLAs
call cli%add(switch='--string',switch_ab='-s',help='String input',required=.true.,act='store',error=error)
call cli%add(switch='--integer',switch_ab='-i',help='Integer input with fixed range',required=.false.,act='store',&
             def='1',choices='1,3,5',error=error)
call cli%add(switch='--real',switch_ab='-r',help='Real input',required=.false.,act='store',def='1.0',error=error)
call cli%add(switch='--boolean',switch_ab='-b',help='Boolean input',required=.false.,act='store_true',def='.false.',&
             error=error)
call cli%add(switch='--boolean_val',switch_ab='-bv',help='Valued boolean input',required=.false., act='store',&
             def='.true.',error=error)
call cli%add(switch='--integer_list',switch_ab='-il',help='Integer list input',required=.false.,act='store',&
             nargs='3',def='1 8 32',error=error)
call cli%add(positional=.true.,position=1,help='Positional real input',required=.false.,def='1.0',error=error)
! parsing CLI
call cli%parse(error=error)
...

For a practical example of FLAP usage see POG source file at line 85.

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