History explains why the octal modes exist, but I think functionality is the reason why the mnemonic form exists. And all the points about other tools using exclusively octal modes are perfectly valid and I think you have to learn and know them. Nevertheless I find that conservative admins don't see the true utility that comes from the mnemonic form.
The octal form, especially when used recursively, tends to force admins to do stupid things. Or rather added negligence results in it turning out stupid. Whenever you run across some folder with a lot of text files and the x
bit set, you have proof.
Why would anyone set the x
bit like that? Because it's difficult not to unless you use the mnemonic form for modes. Consider that you want to reset the permissions on /var/www
and you don't run any old-style CGI, so the x
bit should be removed. However, the x
bit serves another purpose on directories. So you end up doing something (as root
) like:
chmod -R 666 /var/www
find /var/www -type d -exec chmod 777 {} \;
If, however, you were using the mnemonic form you could give it a "recipe":
chmod -R a=rwX /var/www
which is the short form of chmod -R ugo=rwX /var/www
(achieving the same, but different path: chmod -R a-x,a+rwX /var/www
).
But there is another thing that is more trivial which can't be achieved with the octal modes. You cannot adjust the user
or group
or other
mask individually with the octal form.
In short: it's like comparing a scalpel (mnemonic) and a sharp kitchen knife (octal) ... but you still have to know the octal mode bits for other reasons :)
The reason why octal modes are still preferred, I think, is not more typing involved in the mnemonic form, but overly conservative admins. And yes, 2013 calling, those overly conservative admins still exist and are here to stay for some time.