coreutils: Operator Numeric Modes

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1 27.4 Operator Numeric Modes
1 ===========================
1 
1 An operator numeric mode is a numeric mode that is prefixed by a ‘-’,
1 ‘+’, or ‘=’ operator, which has the same interpretation as in symbolic
1 modes.  For example, ‘+440’ enables read permission for the file’s owner
1 and group, ‘-1’ disables execute permission for other users, and ‘=600’
1 clears all permissions except for enabling read-write permissions for
1 the file’s owner.  Operator numeric modes can be combined with symbolic
1 modes by separating them with a comma; for example, ‘=0,u+r’ clears all
1 permissions except for enabling read permission for the file’s owner.
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1    The commands ‘chmod =755 DIR’ and ‘chmod 755 DIR’ differ in that the
1 former clears the directory DIR’s setuid and setgid bits, whereas the
1 latter preserves them.  ⇒Directory Setuid and Setgid.
1 
1    Operator numeric modes are a GNU extension.
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