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<html><head>
<title>Files and Directories</title>
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<body>
<a href="../start.htm">Nyquist / XLISP 2.0</a> -
<a href="../manual/contents.htm">Contents</a> |
<a href="../tutorials/tutorials.htm">Tutorials</a> |
<a href="examples.htm">Examples</a> |
<a href="../reference/reference-index.htm">Reference</a>
<hr>
<h1>Files and Directories</h1>
<hr>
<ul>
<li><nobr>Interactive Functions</nobr></li>
<ul>
<li><nobr><a href="#pwd">pwd</a> - returns the current working directory</nobr></li>
<li><nobr><a href="#cd">cd</a> - changes the current working directory</nobr></li>
</ul>
<li><nobr>Testing Files and Directories</nobr></li>
<ul>
<li><nobr><a href="#directory-exists-p">directory-exists-p</a> - tests if a directory exists</nobr></li>
<li><nobr><a href="#file-exists-p">file-exists-p</a> - tests if a file exists</nobr></li>
<li><nobr><a href="#filename-exists-p">filename-exists-p</a> - tests if a file or directory exists</nobr></li>
</ul>
<li><nobr>Testing Filenames</nobr></li>
<ul>
<li><nobr><a href="#absolute-filename-p">absolute-filename-p</a> - tests if a string is an absolute filename</nobr></li>
</ul>
<li><nobr>System Environment Variables</nobr></li>
<ul>
<li><nobr><a href="#windows-p">windows-p</a> - tests if the operation system is a Windows system</nobr></li>
<li><nobr><a href="#user-home-directory">user-home-directory</a> - returns path to the user's HOME directory</nobr></li>
<li><nobr><a href="#expand-tilde">expand-tilde</a> - replaces "~/" with the user's HOME directory</nobr></li>
</ul>
</ul>
<a name="pwd"></a>
<hr>
<h2>pwd</h2>
<hr>
<p>The 'pwd' function returns the current working directory:</p>
<pre class="example">
(defun <font color="#0000CC">pwd</font> ()
(setdir <font color="#880000">"."</font>))
</pre>
<p>Ok, this function does not belong to the masterpieces of computer
science, but (pwd) is much easier to remember than <nobr>(setdir
".")</nobr>.</p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="cd"></a>
<hr>
<h2>cd</h2>
<hr>
<p>The 'cd' function changes the current working directory. <nobr>The
directory</nobr> name must be given as a string:</p>
<pre class="example">
(defun <font color="#0000CC">cd</font> (string)
(cond ((not (stringp string))
(error <font color="#880000">"argument must be a string"</font> string))
((string= <font color="#880000">"."</font> string)
(setdir <font color="#880000">"."</font>))
(t
(let ((orig-dir (setdir <font color="#880000">"."</font>))
(new-dir (setdir string)))
(when (string/= orig-dir new-dir)
new-dir)))))
</pre>
<p>Possible actions and return values are:</p>
<ul>
<li><p>It the argument is not a string, then an error will be
raised.</p></li>
<li><p>If the directory name is ".", then the name of the current
working directory is returned as a string. This is the same effect as if the
directory has been changed to itself.</p></li>
<li><p>If the directory has successfully been changed to the given
directory, then the name of the new working directory is returned as a
string.</p></li>
<li><p>If the given directory has not been found, then NIL <nobr>[=
false]</nobr> is returned.</p></li>
</ul>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="directory-exists-p"></a>
<hr>
<h2>directory-exists-p</h2>
<hr>
<p>The '<nobr>directory-exists-p</nobr>' function tests if a directory
exists. <nobr>The directory</nobr> name must be given as a string:</p>
<pre class="example">
(defun <font color="#0000CC">directory-exists-p</font> (string)
(cond ((not (stringp string))
(error <font color="#880000">"argument must be a string"</font> string))
((string= <font color="#880000">"."</font> string)
(setdir <font color="#880000">"."</font>))
(t
(let ((orig-dir (setdir <font color="#880000">"."</font>))
(new-dir (setdir string)))
(when (string/= orig-dir new-dir)
(setdir orig-dir)
new-dir)))))
</pre>
<p>Possible actions and return values are:</p>
<ul>
<li><p>It the argument is not a string, then an error will be
raised.</p></li>
<li><p>If the directory name is ".", then the absolute name of the
current working directory is returned as a string. <nobr>This is</nobr> not
a very useful test, but makes the return values consistent.</p></li>
<li><p>If the directory has been found, then the absolute name of the
directory is returned as a string.</p></li>
<li><p>If the directory has not been found, then NIL <nobr>[= false]</nobr>
is returned.</p></li>
</ul>
<p>The '<nobr>directory-exists-p</nobr>' function is nearly the same as the
<a href="#cd">cd</a> function above. <nobr>The only</nobr> difference is
that the working directory will automatically be changed back to the initial
directory.</p>
<p>On Unix, with <nobr>soft-links</nobr>, the absolute name of the target
directory <nobr>[i.e. not</nobr> the name of the <nobr>link-file</nobr>
itself, but the name of the directory the link <nobr>points to]</nobr> is
returned.</p>
<p><div class="box">
<p><b>Implementation Notes</b></p>
<p>The Nyquist 'setdir' function always returns absolute directory names,
even if a relative directory name has been given as a string by the user.
That's why it's not possible to reliably compare the return value of
<nobr>(setdir string)</nobr> directly with 'string'. Instead the absolute
name of the initial working directory, returned by <nobr>(setdir
".")</nobr>, is compared to the absolute name, returned when
<nobr>(setdir string)</nobr> tries to change the directory. <nobr>If
both</nobr> return values are the same, then <nobr>(setdir string)</nobr>
has failed because the directory has not been found.</p>
<p>If the directory string is ".", then this trick doesn't work,
because the initial directory is the same as the target directory, so even
if the directory has 'successfully' been changed to itself, both return
values still would be the same. This is one of the reasons why "."
has a separate 'cond' clause. The other reason is of course that it makes
not really much sense to change a directory to itself, that's why we save
the work and just return the absolute name of the current working
directory.</p>
</div></p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="file-exists-p"></a>
<hr>
<h2>file-exists-p</h2>
<hr>
<p>The '<nobr>file-exists-p</nobr>' function tests if a file exists.
<nobr>The file</nobr> name must be given as a string:</p>
<pre class="example">
(defun <font color="#0000CC">file-exists-p</font> (string)
(if (not (stringp string))
(error <font color="#880000">"argument must be a string"</font> string)
(unless (directory-exists-p string)
(let (file-stream)
(unwind-protect
(setq file-stream (open string))
(when file-stream (close file-stream)))
(when file-stream string)))))
</pre>
<p>On Unix systems a directory is a special kind of file, so on Unix the
XLisp 'open' function can open directories, too. That's why we first must
make sure that no directory exists with the same name as the file that we
are looking for.</p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="filename-exists-p"></a>
<hr>
<h2>filename-exists-p</h2>
<hr>
<pre class="example">
(defun <font color="#0000CC">filename-exists-p</font> (string)
(if (not (stringp string))
(error <font color="#880000">"argument must be a string"</font> string)
(or (directory-exists-p string)
(file-exists-p string)))
</pre>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="absolute-filename-p"></a>
<hr>
<h2>absolute-filename-p</h2>
<hr>
<p>The 'absolute-filename-p' function tests if a string is an absolute file
or directory name:</p>
<pre class="example">
(defun <font color="#0000CC">absolute-filename-p</font> (string)
(if (not (stringp string))
(error <font color="#880000">"argument must be a string"</font> string)
(let ((end (length string)))
(when (or (and (>= end 1) <font color="#008844">; Unix "/..."</font>
(char= #\/ (char string 0)))
(and (>= end 3) <font color="#008844">; Windows "[a-zA-Z]:[\/]..."</font>
(let ((char (char string 0)))
<font color="#008844">;; upper- or lowercase character a-z, A-Z</font>
(and (> (char-code (char-downcase char)) 96)
(< (char-code (char-downcase char)) 123)))
(char= #\: (char string 1))
(let ((char (char string 2)))
(or (char= #\\ char)
(char= #\/ char)))))
string))))
</pre>
<p>Note that it is only tested whether the beginning of the string
matches the beginning of an absolute file or directory name. <nobr>It
is</nobr> not tested whether the string reperesents a meaningful name.</p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="system-environment-variables"></a>
<hr>
<h2>System Environment Variables</h2>
<a name="get-env"></a>
<hr>
<h2>get-env</h2>
<hr>
<p>[This function works only with <nobr>Audacity 1.3.13</nobr> and
above.]</p>
<p><div class="box">
<dl>
<dt><p><nobr>(<b>get-env</b> "<i>environment-variable</i>")</nobr></p></dt>
</dl>
</div></p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="windows-p"></a>
<hr>
<h2>windows-p</h2>
<hr>
<p>[This function works only with <nobr>Audacity 1.3.13</nobr> and
above.]</p>
<p>The '<nobr>windows-p</nobr>' function tests if the underlying operation
system is a Microsoft <nobr>Windows[tm]</nobr> system:</p>
<pre class="example">
(defun <font color="#0000CC">windows-p</font> ()
(let* ((home (let ((drive (get-env <font color="#880000">"HOMEDRIVE"</font>))
(path (get-env <font color="#880000">"HOMEPATH"</font>)))
(if (and drive path)
(strcat drive path)
(get-env <font color="#880000">"UserProfile"</font>))))
(path (get-env <font color="#880000">"PATH"</font>)))
(when home <font color="#008844">; if HOMEDRIVE + HOMEPATH or UserProfile exist</font>
(if path <font color="#008844">; search for Windows :\ drive-letter patterns</font>
(string-search ":\\" path)
(error <font color="#880000">"no PATH environment variable found"</font>)))))
</pre>
<p>Nquist has a <nobr>*file-separator*</nobr> variable, that could be used
much easier to detect the operation system:</p>
<pre class="example">
(defun <font color="#0000CC">windows-p</font> ()
(char= <font color="#AA5500">*file-separator*</font> #\\))
</pre>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="user-home-directory"></a>
<hr>
<h2>user-home-directory</h2>
<hr>
<p>[This function works only with <nobr>Audacity 1.3.13</nobr> and
above.]</p>
<p>The '<nobr>user-home-directory</nobr>' function returns the path to the
user's home directory on Linux, Mac, and Windows:</p>
<pre class="example">
(defun <font color="#0000CC">user-home-directory</font> ()
(or (get-env <font color="#880000">"HOME"</font>)
(let ((drive (get-env <font color="#880000">"HOMEDRIVE"</font>))
(path (get-env <font color="#880000">"HOMEPATH"</font>)))
(when (and drive path)
(strcat drive path)))
(get-env <font color="#880000">"UserProfile"</font>)))
</pre>
<p>If the user's home directory could be identified, then the path to the
home directory is returned as a string. <nobr>If the</nobr> user's home
directory could not be identified, then <nobr>NIL [= false]</nobr> is
returned.</p>
<p>Examples:</p>
<pre class="example">
(user-home-directory) <font color="#444444">=></font> <font color="#008844">"/home/edgar" ; Linux</font>
(user-home-directory) <font color="#444444">=></font> <font color="#008844">"C:\\Documents and Settings\\Edgar" ; Windows</font>
</pre>
<p>On Windows there is no HOME variable defined by Windows itself, but most
programs will respect a HOME variable, if one had been defined by the user.
This means that on Windows, if a HOME variable exists, the HOME variable
will be used instead of HOMEDRIVE and HOMEPATH or 'UserProfile'.</p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="expand-tilde"></a>
<hr>
<h2>expand-tilde</h2>
<hr>
<p>[This function works only with <nobr>Audacity 1.3.13</nobr> and
above.]</p>
<pre class="example">
(defun <font color="#0000CC">expand-filename</font> (string)
(cond ((not (stringp string))
(error <font color="#880000">"argument must be a string"</font> string))
((and (> (length string) 1)
(char= #\~ (char string 0))
(or (char= #\/ (char string 1))
(char= #\\ (char string 1))))
(strcat (user-home-directory)
(subseq string 1)))
(t string)))
</pre>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<hr>
<a href="../start.htm">Nyquist / XLISP 2.0</a> -
<a href="../manual/contents.htm">Contents</a> |
<a href="../tutorials/tutorials.htm">Tutorials</a> |
<a href="examples.htm">Examples</a> |
<a href="../reference/reference-index.htm">Reference</a>
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