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