anchor.diff:      if ( prm_file /= "" ) then
          inquire( file = prm_file, exist = file_exists )
          if ( .not. file_exists ) then
  -          write(0,*) '# ERROR # cannot access '//trim(prm_file)
  +          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)
  +          write(0,*) 'ERROR ! error opening file '//trim(prm_file)
             error_code = 1
             return
          end if
  
positive.code:     if ( rst_file /= "" ) then
         inquire( file = rst_file, exist = file_exists )
         if ( .not. file_exists ) then
            write(0,*) '# ERROR # cannot access '//trim(rst_file)
            error_code = 1
            return
         end if
         call units_open_unf(rst_file,'old',urst,err)
         if( err /= 0 ) then
            write(0,*) '# ERROR # error opening file '//trim(rst_file)
            error_code = 1
            return
         end if
      end if
  
      if (uprm == 0 .and. urst == 0) then
         write(0,*) '# ERROR # either a rst or a prm file'
         error_code = 1
         return
      end if
  
      if( data_file == '' ) then
         write(0,*) '# ERROR # missing datafile'
         error_code = 1
         return
      else
         inquire( file = data_file, exist = file_exists )
         if ( .not. file_exists ) then
            write(0,*) '# ERROR # cannot access '//trim(data_file)
            error_code = 1
            return
         end if
         ! open data file
         call units_open(data_file,'old',udata,err)
         if( err /= 0 ) then
            write(0,*) '# ERROR # error opening file '//trim(data_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
  