Re: wish: chmod -R to handle directories and files differently

[Eric Blake]

On 04/15/2014 05:43 AM, Richard Neill wrote:
> Dear All,
> 
> May I suggest an enhancement to chmod? The problem is that, when using
> chmod -R, the permissions we want to apply to files are usually not the
> same as for directories, especially regarding the executable state.

chmod already has such a feature via the X symbolic mode - you just need
to use it.

> Here are a few ideas for how this could work...
> 
> 1.
> Add a "-d" option that specifies a different permission for directories.
> Eg:
>    chmod -R 644 -d 755 path/to/dir
>    #This sets everything to 644 (as normal for chmod), but treats
>    #directories specially, setting them to 755.

chmod -R u+w,a+rX path/to/dir

give the user write bits, and give all (user, group, and other) the read
bit and conditional executable bit

> 
> 
> 2.
> Add a "-u" option for using the umask. E.g:
>    chmod -R -u path/to/dir
>    #This applies my standard umask, for both files and dirs. It would be
>    #useful for fixing up broken permissions quickly.

chmod -R +rwx path/to/dir

by omitting anything left of the +, this says to use the umask to grant
all permissions allowed by the umask

> 
> 
> 3.
> Add "-D" and -"F" options to mean "apply to directories only" or "apply
> to files only"
> E.g.:
>   chmod -RD  755 /path/to/dir
> recursively sets directories 755, (and leaves files unaltered).
>   chmod -RF  644 /path/to/dir
> recursively sets files to 644, (and leaves directories unaltered).

Here, I'd recommend that you use 'find' rather than bloating chmod further:

find . \( -type d -exec chmod 755 {} + \) -o \( ! -type d -exec chmod
644 {} + \)

> 
> 
> Typical use-cases:
> 
> (a) I have several nested directories of photos that originated from a
> digital camera with a FAT filesystem. Therefore all the directories,
> subdirectories and files are mode 777. I want to remove the executable
> permission from the files, but not the directories.
> 
> =>     chmod -Ru  my/photos/
> 
> (alternative is some ugliness with "find -type d")

Ugly but standardized and universally existing is better than pretty but
unimplemented on the majority of systems.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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