Gnu/coreutils/Copying-Permissions
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27.2.2 Copying Existing Permissions
You can base a file’s permissions on its existing permissions. To do
this, instead of using a series of ‘r
’, ‘w
’, or ‘x
’
letters after the
operator, you use the letter ‘u
’, ‘g
’, or ‘o
’. For
example, the mode
o+g
adds the permissions for users who are in a file’s group to the
permissions that other users have for the file. Thus, if the file
started out as mode 664 (‘rw-rw-r--
’), the above mode would change
it to mode 666 (‘rw-rw-rw-
’). If the file had started out as mode
741 (‘rwxr----x
’), the above mode would change it to mode 745
(‘rwxr--r-x
’). The ‘-
’ and ‘=
’ operations work
analogously.