$ function mkfile () { mkdir -p $(dirname "$@"); touch $@; } 

$ ls /tmp/foo/bar
ls: /tmp/foo/bar: No such file or directory

$ mkfile !:$
mkfile /tmp/foo/bar

$ ls -l /tmp/foo/bar
-rw-r--r-- 1 user user 0 2008-02-04 23:10 /tmp/foo/bar

$