I/O, modules

[thorsopia]

Hello,

Could you show me some trivial programs related to I/O (e.g. read from
file, convert to uppercase, write to another file)?

This page [0] doesn't list a function that can be used to read the whole
file at once. Is there a "read-string" function? What about "read-port"?

Should I import some module to get the above functions? Which one?

BTW, I have a problem with modules. How to check what can be imported?

For example:

I created two files in the same dir:

test-scm.scm:

(define-module (test-scm)
  #:export (test-func))

(define (test-func x)
  (+ x 1))

import-test.scm:

(define-module (import-test)
  #:use-module (test-scm))

(display (test-func 2))

Why does "guile import-test.scm" raise "ERROR: no code for module
(test-scm)"?

[0] https://gnu.org/software/guile/manual/guile.html#Reading