Node:Scripting Examples, Previous:The Top of a Script File, Up:Guile Scripts
To start with, here are some examples of invoking Guile directly:
guile -- a b c
(command-line) will return ("/usr/local/bin/guile" "a" "b" "c").
guile -s /u/jimb/ex2 a b c
/u/jimb/ex2; (command-line) will return ("/u/jimb/ex2" "a" "b" "c").
guile -c '(write %load-path) (newline)'
%load-path, print a newline,
and exit.
guile -e main -s /u/jimb/ex4 foo
/u/jimb/ex4, and then call the function
main, passing it the list ("/u/jimb/ex4" "foo").
guile -l first -ds -l last -s script
first, script, and last, in that
order. The -ds switch says when to process the -s
switch. For a more motivated example, see the scripts below.
Here is a very simple Guile script:
#!/usr/local/bin/guile -s !# (display "Hello, world!") (newline)The first line marks the file as a Guile script. When the user invokes it, the system runs
/usr/local/bin/guile to interpret the script,
passing -s, the script's filename, and any arguments given to the
script as command-line arguments. When Guile sees -s
script, it loads script. Thus, running this program
produces the output:
Hello, world!
Here is a script which prints the factorial of its argument:
#!/usr/local/bin/guile -s
!#
(define (fact n)
(if (zero? n) 1
(* n (fact (- n 1)))))
(display (fact (string->number (cadr (command-line)))))
(newline)
In action:
$ fact 5 120 $
However, suppose we want to use the definition of fact in this
file from another script. We can't simply load the script file,
and then use fact's definition, because the script will try to
compute and display a factorial when we load it. To avoid this problem,
we might write the script this way:
#!/usr/local/bin/guile \
-e main -s
!#
(define (fact n)
(if (zero? n) 1
(* n (fact (- n 1)))))
(define (main args)
(display (fact (string->number (cadr args))))
(newline))
This version packages the actions the script should perform in a
function, main. This allows us to load the file purely for its
definitions, without any extraneous computation taking place. Then we
used the meta switch \ and the entry point switch -e to
tell Guile to call main after loading the script.
$ fact 50 30414093201713378043612608166064768844377641568960512000000000000
Suppose that we now want to write a script which computes the
choose function: given a set of m distinct objects,
(choose n m) is the number of distinct subsets
containing n objects each. It's easy to write choose given
fact, so we might write the script this way:
#!/usr/local/bin/guile \
-l fact -e main -s
!#
(define (choose n m)
(/ (fact m) (* (fact (- m n)) (fact n))))
(define (main args)
(let ((n (string->number (cadr args)))
(m (string->number (caddr args))))
(display (choose n m))
(newline)))
The command-line arguments here tell Guile to first load the file
fact, and then run the script, with main as the entry
point. In other words, the choose script can use definitions
made in the fact script. Here are some sample runs:
$ choose 0 4 1 $ choose 1 4 4 $ choose 2 4 6 $ choose 3 4 4 $ choose 4 4 1 $ choose 50 100 100891344545564193334812497256