CoCreate Modeling code examples: A platform-independent ls -l replacement

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---++ <nop>CoCreate Modeling: A platform-independent ls -l replacement

Oftentimes, users overlook the wealth of file handling functionality which is built-in
into Common Lisp and also into <nop>CoCreate Modeling's dialect of the language. Way too often,
it is assumed that any kind of OS-level work should best be done by calling
external components, for example by running DOS or UNIX utilities via a command
shell. If you need access to external utilities, =oli:sd-sys-exec= is your friend,
but as a rule of thumb, if you're using =oli:sd-sys-exec=, chances are that there are
much better and less platform-dependent ways to achieve the same.

As an example, here is some code which does the rough equivalent of
<pre>
  ls -l /some/directory/*somepattern* >somelogfile
</pre>

Sure enough, the command-line above looks simple and takes only a few seconds
to type, but it simply doesn't port to non-UNIX systems (except if you install
a UNIX-like shell environment on them). Here's a platform-independent
approximation:

<pre>
;; -*-Lisp-*-
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Description:  Platform-independent replacement for ls -l
;; Author:       Claus Brod  
;; Language:     Lisp
;;
;; (C) Copyright 2005 Claus Brod, all rights reserved
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
(in-package :clausbrod.de)
(export 'ls-l)

(defun file-mod-time(f)
  (multiple-value-bind (sec minutes hour date month year)
      (decode-universal-time (file-write-date f))
    (format nil "~D/~2,'0D/~2,'0D ~2,'0D:~2,'0D:~2,'0D" year month date hour minutes sec)))

(defun print-file-info(s f)
  (format s "~A ~A ~A~%" (file-namestring f) (file-mod-time f) 
     (oli:sd-inq-file-size (file-namestring f))))

(defun ls-l(dir pattern logfile)
  (oli:sd-with-current-working-directory dir
   (with-open-file (s logfile :direction :output :if-exists :supersede)
     (dolist (f (directory pattern))
       (print-file-info s f)))))
</pre>

Usage example:
<pre>
  (clausbrod.de:ls-l "c:/temp" "*.pkg" "pkg.log")
</pre>

It's too bad that Common Lisp doesn't have a direct equivalent of
[[http://www.opengroup.org/onlinepubs/007908799/xsh/strftime.html][strftime]] - this
would have saved me from <tt>format</tt>'s funky parameter syntax. But still, now
we've got code which...
   * ... is platform-independent,
   * ... does not need to fork costly external processes to do its job,
   * ... is adaptable to particular formatting requirements, unlike
         external utilities such as =dir= or =ls=, where you have to
         live with the way they format their output
         and somehow cope with it.

-- Main.ClausBrod - 11 Oct 2005

%COMMENT{type="below" nonotify="on"}%
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