Common Lisp Tips

Touching a file

To create an empty file, like the Unix touch command does, you might try something like this:

;; BOGUS
(close (open "foo.txt" :direction :output 
             :if-does-not-exist :create 
             :if-exists :append))

open has a :direction option specifically for this purpose, though:

(open "foo.txt" :direction :probe :if-does-not-exist :create)

If “foo.txt” does not exist, it will be created. The stream returned is already closed. The spec says this:

[:probe causes] the creation of a “no-directional” file stream; in effect, the file stream is created and then closed prior to being returned by open.