FLAP Documentation

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FLAPFortran command Line Arguments Parser for poor people

A KISS pure Fortran 2003+ library for building powerful, elegant Command Line Interfaces — inspired by Python's argparse

Guide
API Reference
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🖥️

Argparse-style API

Define your CLI with a handful of method calls. FLAP automatically generates help, usage, and version messages — no boilerplate.

✅

Rich argument types

Optional, required, boolean, positional, list-valued (fixed or runtime-sized), choices-constrained, and environment-variable arguments.

🔀

Nested subcommands

Build git-style interfaces with named command groups, each with their own arguments and auto-generated per-command help.

🔒

Mutually exclusive arguments

Declare argument pairs or entire command groups that cannot be used together — with automatic error reporting.

📄

Multiple output formats

Export your CLI as a man page, bash completion script, or Markdown usage page with a single method call.

🆓

Free & Open Source

Multi-licensed — GPLv3 for FOSS projects, BSD 2/3-Clause or MIT for commercial use. Fortran 2003+ standard compliant.

Quick start ​

A minimal plate:

fortran
program minimal
type(command_line_interface) :: cli    ! Command Line Interface (CLI).
character(99)                :: string ! String value.
integer                      :: error  ! Error trapping flag.

call cli%init(description = 'minimal FLAP example')
call cli%add(switch='--string', &
             switch_ab='-s',    &
             help='a string',   &
             required=.true.,   &
             act='store',       &
             error=error)
if (error/=0) stop
call cli%get(switch='-s', val=string, error=error)
if (error/=0) stop
print '(A)', cli%progname//' has been called with the following argument:'
print '(A)', 'String = '//trim(adjustl(string))
endprogram minimal

Authors ​

Contributions are welcome — see the Contributing page.

Copyrights ​

This project is distributed under a multi-licensing system:

Anyone interested in using, developing, or contributing to this project is welcome — pick the license that best fits your needs.