group ID
  -G, --groups   print all group IDs
  -n, --name     print a name instead of a number, for -u,-g,-G
  -r, --real     print the real ID instead of the effective ID, with -u,-g,-G
  -u, --user     print only the effective user ID
  -z, --zero     delimit entries with NUL characters, not whitespace;
                   not permitted in default format
