Features

Argument Types

FLAP supports every argument style commonly found in Unix CLIs:

Type	Description
Optional switch	--verbose / -v; not required, has a default
Required switch	--output file; error if missing
Boolean flag	store_true / store_false; no value consumed
Positional	unnamed, matched by position
List-valued	fixed nargs=N or runtime nargs='+' / nargs='*'
Choices-constrained	value must be one of a predefined set
Environment-variable	falls back to an env var when the switch is absent
Hidden	registered but not shown in help output

Subcommands

Build git-style interfaces by grouping arguments into named command groups. Each group has its own argument list and gets its own auto-generated help page:

call cli%add_group(group='commit', description='Record changes to the repository')
call cli%add(group='commit', switch='--message', switch_ab='-m', ...)

Use cli%run_command(group) to discover which subcommand was selected at runtime. Entire groups can be declared mutually exclusive with set_mutually_exclusive_groups.

Output Formats

FLAP can export your CLI definition in several formats with a single call:

Method	Output
cli%usage()	Formatted help/usage string (printed automatically on error)
cli%save_man_page(unit)	Unix man page (troff format)
cli%save_bash_completion(unit)	Bash tab-completion script
cli%save_usage_to_markdown(unit)	Markdown usage documentation

The Four-Step Pattern

Every FLAP program follows the same four steps:

use flap
implicit none

type(command_line_interface) :: cli
integer                      :: error

! 1. Initialise the CLI
call cli%init(progname='myprogram', description='Does something useful')

! 2. Add argument definitions
call cli%add(switch='--output', switch_ab='-o', &
             help='Output file', required=.true., act='store', error=error)
if (error /= 0) stop

! 3. Parse the command line
call cli%parse(error=error)
if (error /= 0) stop

! 4. Retrieve values
character(256) :: outfile
call cli%get(switch='-o', val=outfile, error=error)
if (error /= 0) stop

Module Architecture

flap.f90                               ← public interface (use this in consuming code)
└── flap_command_line_interface_t.F90  ← main CLI type
    ├── flap_command_line_arguments_group_t.f90  ← groups / subcommands
    │   └── flap_command_line_argument_t.F90     ← individual argument
    │       ├── flap_object_t.F90                ← base class (error handling)
    │       └── flap_utils_m.f90
    └── (PENF — numeric precision kinds)
    └── (FACE — ANSI terminal colours)

Any feature request is welcome — open an issue on GitHub.