[PLUG] -R vs. find(1) + xargs(1)

[gabriel rosenkoetter <gr@eclipsed.net>]

I let it slide at to(last?)night's meeting, but here's the number 1
reason you never want to use -R (there are others): -R will follow
sym links, whereas you can always tell find(1) not to.

Suppose you're moving a bunch of users from one system to another.
uids conflict, so you'll have to chown and chgrp (if you think you
don't need to chgrp, you must not have any users sharing files, or
no conflict gids for those shared groups) all over /home (or
equivalent; while I'm at it, if you're on Solaris and you think you
can get away with chown and chgrp at all rather than setfacl, you'll
lose). You do it with -R, and Joe "Local Root" Cracker has a sym
link to /etc/shadow in his home directory. Whoops. Then you realize
you missed the dot-files and do -R on .*. Yikes. Go find a tape
backup (you've got one, of course?): you're hosed.

Note that some ch{mod,grp,own}(1)s have a -P flag which says "never
follow sym links". That's nice. It's probably even a Posix standard.
I don't trust it. Sun's stuff, for instance, still lacks it in
Solaris 8 (and Solaris 9, I think, though I don't have a copy around
any more to check). No, you don't want to use GNU's utilities for
this on Solaris (or FreeBSD, btw), as they'll mangle ACLs.

In any case, the point is that recursion should scare you a lot in
file systems. You should take the time to make sure it won't hurt
anything. But that's time you could take just thinking of all the
cases (there really aren't that many) and constructing a proper find
| xargs command line.

(On a related note, you *really* want to use GNU find(1)'s -print0
and their xargs(1) -0 flags. You want to use them badly enough to
install them on Sun systems, which still lack these intensely useful
features. Especially where Samba and users unaware of Unix naming
conventions are involved. You may not need them every time, but
the first time you needed them and didn't use them, you'll know that
you really just want to use them all the time and not repeat the
agony.)

-- 
gabriel rosenkoetter
gr@eclipsed.net

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