read the whole file into a string?

Hi,

A simple question, how to read a file into one single string? I looked into
the manuals of scsh, only found this:

(read-string nbytes [fd/port])     --->     string or #f (procedure)
(read-string! str [fd/port start end]) --->     nread or #f (procedure)

I took a try:

(let* ((port (open-file "/tmp/foo" open/read))
       (str (read-string 100 port)))
  (display str))

Can someone give me a hint? 

thanks.

--
William