anchor.diff:  
       if (nargs == 0) then
          ! no args: print syntax and stop
  -       write(0,*) trim(syntax)
  +       write(0,100)
          error_code = 1
          return
       end if
  
positive.code:   implicit none
    private
    public :: command_line_read
    character(len=1), parameter                  :: nl=achar(10)
    character(len=long_string_size)              :: syntax = nl//& 
         '                                       elss-sample (v0.3.1)                                    '//nl//&
         '                                    ==========================                                 '//nl//&
         nl//&
         nl//&
         'Option                         Description                                     (Default Value)  '//nl//&
         '------------------------------------------------------------------------------------------------'//nl//&
         ' (-p|--prm) <path_to_file>     parameters file                                 (None)           '//nl//&   
         '        OR'//nl//&   
         ' (-c|--chk) <path_to_file>     checkpoint file                                 (None)           '//nl//&   
         nl//&
         nl//&
         ' (-h|--help)                   print this help message                         (None)           '//nl//&
         nl//&
         ' --prefix <strin               prefix for output files                         (None)           '//nl//&
         nl//&
         ' (-n|--nsweeps) <int>          num. of MC sweeps                               (1000)           '//nl//&
         nl//&
         ' (-u|--nupdate) <int>          stride (as num. of sweeps) for averages updates (10)             '//nl//&
         nl//&
         ' (-s|--seq) <path_to_file>     starting sequence file                          (None)           '//nl//&
         nl//&
         ' --seed <int>           init. the random seed (if 0, use system_clock)  (0)              '//nl//&
         '------------------------------------------------------------------------------------------------'//nl//&
         nl//&
         nl//&
         '------------------------------------------------------------------------------------------------'//nl//&
         ' For more information and usage examples, please check the project github repository:           '//nl//&
         ' https://github.com/simomarsili/elss                                                            '//nl//&
         '------------------------------------------------------------------------------------------------'//nl//&
         '                                                                                                    '
  contains
  
    subroutine command_line_read(uprm,uchk,useq,rseed,beta,mc_nsweeps,nupdate,&
  
negative.code:        select case(trim(arg))
         case('-h','--help')
            ! print help and exit
            write(0,100)
            error_code = 1
            return
         case('-p','--prm')
  