2006-12-05
A small annoyance with Unix wildcards
Here's a small irritation with Unix wildcards: there's no generally
recognized wildcard (or small set of wildcards) that matches all of the
files in a directory, including dotfiles but excluding . and ..,
so that you could easily match all of a directory's real contents.
A plain * doesn't match dotfiles; * .* matches dotfiles, but
includes . and .. too. About the best you can do is
* .??* .[^.]
However this blows up if there's no single-character dotfiles. This is a general defect in any multi-wildcard scheme, of course; the more wildcards and the more obscure they are, the more likely you are to have one that doesn't match anything.
I believe that some shells have a .* wildcard that doesn't include .
and ..; on quick testing, zsh is one. (Bash and ksh seem almost able
to do it but not quite, as far as I can tell.)
Interestingly, the behavior of * not matching files that start
with . goes back at least as far as V5 Unix. (The V4 Unix sources
have apparently been lost, and the V4 and V5 manpages are not
precise enough to say whether the behavior existed in V4. If you
are poking around this stuff at tuhs.org,
it is helpful to know that in V6 and earlier shell globbing was
done by an external program, /etc/glob; the V5 source is here.)
It's interesting to see that fairly complete shell wildcard support goes
back very far in Unix history. Third Edition, released in February
1973 and the oldest Unix that tuhs.org has useful stuff for, already
has *, ?, and [...] (including character ranges with -).
(Since the V3 ls has a -a option to reveal dotfiles, I suspect that
even V3 * wildcards didn't match dotfiles.)
Bonus trivia: the oldest ls options, present in V3, are -l, -t,
-a, -s, and -d. V4 ls grew -r and -u, and after that you
can go digging for yourself.