用法：chgrp [选项]… 用户组 文件…
　或：chgrp [选项]… --reference=参考文件 文件…
Change the group of each FILE to GROUP.
With --reference, change the group of each FILE to that of RFILE.

-c, --changes like verbose but report only when a change is made
-f, --silent, --quiet suppress most error messages
-v, --verbose output a diagnostic for every file processed
–dereference affect the referent of each symbolic link (this is
the default), rather than the symbolic link itself
-h, --no-dereference affect symbolic links instead of any referenced file
(useful only on systems that can change the
ownership of a symlink)
–no-preserve-root do not treat ‘/’ specially (the default)
–preserve-root fail to operate recursively on ‘/’
–reference=RFILE use RFILE’s group rather than specifying a
GROUP value
-R, --recursive operate on files and directories recursively

The following options modify how a hierarchy is traversed when the -R
option is also specified. If more than one is specified, only the final
one takes effect.

-H if a command line argument is a symbolic link
to a directory, traverse it
-L traverse every symbolic link to a directory
encountered
-P do not traverse any symbolic links (default)

  --help		显示此帮助信息并退出--version		显示版本信息并退出

示例：
chgrp staff /u 将 /u 的属组更改为"staff"。
chgrp -hR staff /u 将 /u 及其子目录下所有文件的属组更改为"staff"。