`chmod` changes mode of all files specified in `path` to `octal-mode` or using symbolic representation.
The symbolic representation format is `[[ugoa][+-=][rwx...],...]`. Multiple symbolic can be given, separated by commas.
The letters `[ugoa]` controls which users' access will be changes: `u` means file owner, `g` file owning group, `o` others, and `a` - all users. If no letter is given, `a` is assumed.
The letters `[+-=]` controls which action will be taken: `+` sets the permission, `-` removes the permission, and `=` sets the mentioned permissions and unsets the other permissions.
The letters `[rwx]` controls which permission will be changes: `r` is read, `w` is write and `x` is execute.
A numeric mode is combination of 1 to 4 numbers. Omitted digits are assumed to be leading zeros. The first digit select the set user ID (4), set group ID (2) and restricted deletion / sticky (1) attributes. The second, third and fourth digit controls permissions of each user group: owner, owning group and others (not owner or owning group), respectively: read (4), write (2) and execute (1).