Usage: XXXXXXX [options] NAME1 NAME2

  Xn, XXnormal     Output Normal format (default)
  Xu, XXunified    Output Unified format
  Xb, XXbrief      Report only if NAMEs differ or not
  Xe, XXempty      Treat absent files as empty
  Xr, XXrecurse    Recurse subdirectories
  Xt, XXtwocol     Show two-column output
  Xw, XXwidth N    Column width of two-column output
  Xg, XXgloss      Prefix line with char indicating change
  Xs, XXspace      Ignore space and tab differences
  Xl, XXlineend    Ignore line ending
  Xa, XXalt CHARS  Set alternate chars
  Xq, XXquiet      Suppress normal output
  Xh, XXhelp       Show this help
  Xv, XXversion    Show version
  Xd, XXdata       Show data structure (for developer)

NAME1 and NAME2 must either both be files or both be directories.
CHARS is 1-6 chars which replace corresponding chars in the string '<>+-=%' and
may need to be quoted to prevent shell interpretation or if spaces are used.
Exit status is 0 if inputs are the same, 1 if different, 2 if trouble.
