dtopen.gsf

* cmd: open command (if necessary)
function dtopen( dir, tail, cmd, error )
  ret = read( dir'/'tail  )
  stat = sublin( ret, 1 )
  if( stat = 0 )
    fv_pre = last()

    if( cmd = 'cmd' | cmd = '' )
      'xopen 'dir'/'tail
    else
      cmd' 'dir'/'tail
    endif
    fv = last()
    if( fv = fv_pre )
      fv = -1
    else
      say 'open #' % fv % ': ' % dir % '/' % tail
    endif
  else
    fv = -1
  endif

  if( error != 0 & fv < 0 )
    say 'error: fail to open ' % dir % '/' % tail
    exit
  endif
  if( fv < 0 )
    say 'info: fail to open ' % dir % '/' % tail
  endif
return fv