(coreutils.info)groups invocation

20.4 `groups': Print group names a user is in
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`groups' prints the names of the primary and any supplementary groups
for each given USERNAME, or the current process if no names are given.
If names are given, the name of each user is printed before the list of
that user's groups.  Synopsis:

     groups [USERNAME]...

   The group lists are equivalent to the output of the command `id -Gn'.

   The only options are `--help' and `--version'.  Note: Common
options.

   An exit status of zero indicates success, and a nonzero value
indicates failure.