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(guile.info)The Top of a Script File

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The Top of a Script File
------------------------

The first line of a Guile script must tell the operating system to use
Guile to evaluate the script, and then tell Guile how to go about doing
that.  Here is the simplest case:

   * The first two characters of the file must be `#!'.

     The operating system interprets this to mean that the rest of the
     line is the name of an executable that can interpret the script.
     Guile, however, interprets these characters as the beginning of a
     multi-line comment, terminated by the characters `!#' on a line by
     themselves.  (This is an extension to the syntax described in
     R5RS, added to support shell scripts.)

   * Immediately after those two characters must come the full pathname
     to the Guile interpreter.  On most systems, this would be
     `/usr/local/bin/guile'.

   * Then must come a space, followed by a command-line argument to
     pass to Guile; this should be `-s'.  This switch tells Guile to
     run a script, instead of soliciting the user for input from the
     terminal.  There are more elaborate things one can do here; see
     Note: The Meta Switch.

   * Follow this with a newline.

   * The second line of the script should contain only the characters
     `!#' -- just like the top of the file, but reversed.  The
     operating system never reads this far, but Guile treats this as
     the end of the comment begun on the first line by the `#!'
     characters.

   * The rest of the file should be a Scheme program.


Guile reads the program, evaluating expressions in the order that they
appear.  Upon reaching the end of the file, Guile exits.

The function `command-line' returns the name of the script file and any
command-line arguments passed by the user, as a list of strings.

For example, consider the following script file:
     #!/usr/local/bin/guile -s
     !#
     (write (command-line))
     (newline)

If you put that text in a file called `foo' in the current directory,
then you could make it executable and try it out like this:
     $ chmod a+x foo
     $ ./foo
     ("./foo")
     $ ./foo bar baz
     ("./foo" "bar" "baz")
     $

As another example, here is a simple replacement for the POSIX `echo'
command:
     #!/usr/local/bin/guile -s
     !#
     (for-each (lambda (s) (display s) (display " "))
       (cdr (command-line)))
     (newline)

 - procedure: command-line
 - primitive: program-arguments
     Return a list of the command-line arguments passed to the currently
     running program.  If the program invoked Guile with the `-s', `-c'
     or `--' switches, these procedures ignore everything up to and
     including those switches.