Why can’t bash recognize the existence of a socket file

On a Linux box I want to check if a specific socket file exists. I know the socket files exists, but my checks in bash don’t show that to me:

$ ls -l /var/run/supervisor.sock
srwxrw-rw- 1 root root 0 Jun  3 13:30 /var/run/supervisor.sock  # <== THE FILE EXISTS!!
$ if [ ! -f /var/run/supervisor.sock ]; then echo 'file does not exist!'; fi
file does not exist!

Why oh why can’t bash see that the file exists?

Answer

http://www.tldp.org/LDP/abs/html/fto.html

Use -S to test if its a socket. -f is for regular files.

See man 1 test:

   -e FILE
          FILE exists
   -f FILE
          FILE exists and is a regular file
   ...
   ...
   -S FILE
          FILE exists and is a socket