A bit more on this.

Files exists independently of directory entries in unix. Think of them as being referenced-counted. They exist as long as they are referenced by a directory entry or by a file handle.

This means you can have "anonymous files". perl -i uses this (which is why it doesn't work on Windows without an extension). File::Temp creates these by default.

ls -l even shows how many times a file is referenced by a directory entry (second column). For plain files, it's usually one. For directories, it should be more than one.

$ ls -ld . .. .bash* bin usr
drwxr-xr-x 10 ikegami ikegami 4096 Feb 19 23:53 ./
drwxr-xr-x  3 root    root    4096 Dec 10 21:14 ../
-rw-------  1 ikegami ikegami  163 Jan  3 02:07 .bash_logout
-rw-------  1 ikegami ikegami 2318 Jan  3 02:07 .bashrc
-rw-------  1 ikegami ikegami    0 Jan  3 02:07 .bashrc_extra
drwx------  2 ikegami ikegami 4096 Feb 14 12:13 bin/
drwx------  3 ikegami ikegami 4096 Jan 24 15:39 usr/
[download]

See how .. is referenced by three directory entries? Those are /home, /home/. and /home/ikegami/..

See how . is referenced by ten directory entries? Those are /home/ikegami, /home/ikegami/., /home/ikegami/bin/.., /home/ikegami/usr/.., etc.