anchor.diff:            ! prm file
             call read_arg(iarg,nargs,prm_file,err)
             if (err == 1) then
  -             write(0,*) '# ERROR # missing argument: '//trim(arg)//' <filename>'
  +             write(0,*) 'ERROR ! missing argument: '//trim(arg)//' <filename>'
                error_code = 1
                return
             end if
  
positive.code:     if ( prm_file /= "" ) then
         inquire( file = prm_file, exist = file_exists )
         if ( .not. file_exists ) then
            write(0,*) '# ERROR # cannot access '//trim(prm_file)
            error_code = 1
            return
         end if
         call units_open(prm_file,'old',uprm,err)
         if( err /= 0 ) then
            write(0,*) '# ERROR # error opening file '//trim(prm_file)
            error_code = 1
            return
         end if
  
negative.code:           ! rst file
            call read_arg(iarg,nargs,rst_file,err)
            if (err == 1) then
               write(0,*) 'ERROR ! missing argument: '//trim(arg)//' <filename>'
               error_code = 1
               return
            end if
         case default
            write(0,*) 'ERROR ! invalid option '//trim(arg)
            error_code = 1
            return
         end select
      end do args_loop
  
      if (prm_file /= "" .and. rst_file /= "") then
         write(0,*) 'ERROR ! either a rst or a prm file'
         error_code = 1
         return
      end if
  