Parsing Command Line Arguments with Fortran

To evaluate the arguments your program got on the command line, there are two runtime calls available: A small Fortran 90 program demonstrates their usage:
      program getarg_example
        implicit none
        integer :: i, argc, iargc
        character(len=80) :: arg

        argc=iargc()
        write(6,*) argc

        do i=1, argc
          call getarg(i, arg)
          write(6,*) trim(arg)
          ! read(arg,'(i)') some_integer
          ! read(arg,'(f)') some_real_or_double
          ! etc...
        end do
      end program
This is somewhat clumsy in its usage. So I wrote a Fortran 90 module which behaves like the C function getopt. getoptions.f90:
! This software is distributed under the following terms:
! 
! Copyright (C) 2005 Dominik Epple
! 
! Redistribution and use in source and binary forms, with or without
! modification, are permitted provided that the following conditions
! are met:
! 1. Redistributions of source code must retain the above copyright
!    notice, this list of conditions and the following disclaimer.
! 2. Redistributions in binary form must reproduce the above copyright
!    notice, this list of conditions and the following disclaimer in the
!    documentation and/or other materials provided with the distribution.
! 
! THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS `AS IS' AND
! ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
! IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
! ARE DISCLAIMED.  IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
! FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
! DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
! OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
! HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
! LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
! OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
! SUCH DAMAGE.

      module getoptions
        implicit none
        save
        character(len=80) :: optarg
        integer :: optind=1

        ! this variable should be module private - no plan how to do that
        integer :: optstr_ind
        contains
          character function getopt(optstr)
            character(len=*),intent(IN) :: optstr

            integer :: argc
            character(len=80) :: arg
            character :: okey
            integer :: found

            integer :: iargc
            argc=iargc()
            if(optind.gt.argc) then
              getopt='>'
              return
            end if
            call getarg(optind, arg)
            if(arg(1:1).eq.'-') then
              okey=arg(2:2)
              found=0
              optstr_ind=1
              do while(optstr_ind.le.6)
                if(optstr(optstr_ind:optstr_ind).eq.okey) then
                  found=1
                  if(optstr(optstr_ind+1:optstr_ind+1).eq.':') then
                    optstr_ind=optstr_ind+1
                    optind=optind+1
                    call getarg(optind, optarg)
                  end if
                  exit
                end if
                optstr_ind=optstr_ind+1
              end do
              if(found.gt.0) then
                getopt=okey
              else
                getopt='!'
                optarg=arg
              end if
            else
              getopt='.'
              optarg=arg
            end if
            optind=optind+1
            return
          end function
      end module

This module implements only a small subset of standard C getopt. The following forms of arguments are allowed: Thus, the following command line can be parsed with the module (given the correct optstr):
% ./a.out -b -d 2.3d0 -i 15 -r 1.2 -o file.out file.in
Grouping of arguments is not allowed.

A sample program follows: use_getoptions.f90

! This software is distributed under the following terms:
! 
! Copyright (C) 2005 Dominik Epple
! 
! Redistribution and use in source and binary forms, with or without
! modification, are permitted provided that the following conditions
! are met:
! 1. Redistributions of source code must retain the above copyright
!    notice, this list of conditions and the following disclaimer.
! 2. Redistributions in binary form must reproduce the above copyright
!    notice, this list of conditions and the following disclaimer in the
!    documentation and/or other materials provided with the distribution.
!
! THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS `AS IS' AND
! ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
! IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
! ARE DISCLAIMED.  IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
! FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
! DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
! OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
! HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
! LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
! OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
! SUCH DAMAGE.

      program use_getoptions
        use getoptions
        implicit none

        character :: okey

        character(len=80) :: filename='def.in', ofilename='def.out'
        integer :: i=1
        integer :: binary=0
        double precision :: d=0
        real :: r=0

        write(6,*)
        write(6,*) 'Parsing arguments and parameters:'
        write(6,*) '---------------------------------'
        write(6,*)

        do
          okey=getopt('i:br:d:o:')
          if(okey.eq.'>') exit
          if(okey.eq.'!') then
            write(6,*) 'unknown option: ', trim(optarg)
            stop
          end if
          if(okey.eq.'b') then
            binary=1
            write(6,*) 'Found argument: -',okey
          end if
          if(okey.eq.'i') then
            read(optarg,'(i)') i
            write(6,*) 'Found argument: -',okey,' with value ',trim(optarg)
          end if
          if(okey.eq.'d') then
            read(optarg,'(f)') d
            write(6,*) 'Found argument: -',okey,' with value ',trim(optarg)
          end if
          if(okey.eq.'o') then
            ofilename=optarg
            write(6,*) 'Found argument: -',okey,' with value ',trim(optarg)
          end if
          if(okey.eq.'r') then
            read(optarg,'(f)') r
            write(6,*) 'Found argument: -',okey,' with value ',trim(optarg)
          end if
          if(okey.eq.'.') then
            filename=optarg
            write(6,*) 'Found parameter: ',trim(filename)
          end if
        end do

        write(6,*)
        write(6,*) 'Got these arguments and parameters:'
        write(6,*) '-----------------------------------'
        write(6,*)

        write(6,*) 'binary:',binary
        write(6,*) 'integer:',i
        write(6,*) 'double:',d
        write(6,*) 'real:', r
        write(6,*) 'filename:',trim(filename)
        write(6,*) 'ofilename:',trim(ofilename)
      end program

This program demonstrates the usage of getopt: It is being called repeatedly until it returns '>' to indicate all arguments have been processed.

The argument to getopt is the optstr, which contains the valid options, followed by a colon if the options takes an argument.

getopt returns

After calling getopt the module variable optarg (a string) contains the value of the argument, or the parameter, or the option itself if an invalid option has been found, in the form -x.

You can convert the string optarg to a real value with read(optarg,'(f)') r, and analogously to integer, double precision etc.

Impressum

Contact the author.