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4.9 KiB
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87 lines
4.9 KiB
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<!DOCTYPE HTML PUBLIC "-//W3O//DTD W3 HTML 2.0//EN">
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<!Converted with LaTeX2HTML 0.6.5 (Tue Nov 15 1994) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds >
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<HEAD>
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<TITLE>23.5. Accessing Directories</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" Accessing Directories">
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<meta name="keywords" value="clm">
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<meta name="resource-type" value="document">
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<meta name="distribution" value="global">
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<P>
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<b>Common Lisp the Language, 2nd Edition</b>
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<BR> <HR><A NAME=tex2html4274 HREF="node219.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html4272 HREF="node202.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html4268 HREF="node217.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html4276 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html4277 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html4275 HREF="node219.html"> Errors</A>
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<B>Up:</B> <A NAME=tex2html4273 HREF="node202.html"> File System Interface</A>
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<B> Previous:</B> <A NAME=tex2html4269 HREF="node217.html"> Loading Files</A>
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<HR> <P>
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<H1><A NAME=SECTION002750000000000000000>23.5. Accessing Directories</A></H1>
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<P>
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The following function is a very simple portable primitive for examining
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a directory. Most file systems can support much more powerful
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directory-searching primitives, but no two are alike.
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It is expected that most implementations of Common Lisp will extend the
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<tt>directory</tt> function or provide more powerful
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primitives.
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<P>
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<BR><b>[Function]</b><BR>
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<tt>directory <i>pathname</i> &key</tt><P>A list of pathnames is returned, one for each
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file in the file system that matches the given <i>pathname</i>.
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(The <i>pathname</i> argument may be a pathname, a string,
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or a stream associated with a file.)
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For a file that matches, the <tt>truename</tt> appears
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in the result list.
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If no file matches the <i>pathname</i>, it is not an error;
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<tt>directory</tt> simply returns <tt>nil</tt>, the list of no results.
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Keywords such as <tt>:wild</tt> and <tt>:newest</tt> may
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be used in <i>pathname</i> to indicate the search space.
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<P>
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<img align=bottom alt="change_begin" src="gif/change_begin.gif"><br>
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X3J13 voted in March 1988
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(PATHNAME-STREAM) <A NAME=27783> </A>
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to specify exactly which streams may be used as pathnames.
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See section <A HREF="node214.html#PATHNAMEFUNCTIONS">23.1.6</A>.
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<P>
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X3J13 voted in January 1989
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(CLOSED-STREAM-OPERATIONS) <A NAME=27787> </A>
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to specify that <tt>directory</tt> is unaffected by
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whether the first argument, if a stream, is open or closed. If the first
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argument is a stream, <tt>directory</tt> behaves as if the function <tt>pathname</tt>
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were applied to the stream and the resulting pathname used instead.
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However, X3J13 commented that the treatment of open streams
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may differ considerably from one implementation to another; for example,
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in some operating systems open files are written under a temporary or
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invisible name and later renamed when closed. In general, programmers writing
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code intended to be portable should be careful when using <tt>directory</tt>.
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<P>
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X3J13 voted in June 1989 (PATHNAME-LOGICAL) <A NAME=27794> </A> to require <tt>directory</tt>
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to accept logical pathnames (see section <A HREF="node208.html#LOGICALPATHNAMESSECTION">23.1.5</A>).
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However, the result returned by <tt>directory</tt> never contains a logical pathname.
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<br><img align=bottom alt="change_end" src="gif/change_end.gif">
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<P>
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<hr>
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<b>Implementation note:</b> It is anticipated that
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an implementation may need to provide additional
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parameters to control the directory search. Therefore <tt>directory</tt>
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is specified to take additional keyword arguments so that implementations
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may experiment with extensions,
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even though no particular keywords are specified here.
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<P>
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As a simple example of such an extension, for a file system that
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supports the notion of cross-directory file links,
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a keyword argument <tt>:links</tt> might, if non-<tt>nil</tt>,
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specify that such links be included in the result list.
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<hr>
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<P>
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<BR> <HR><A NAME=tex2html4274 HREF="node219.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html4272 HREF="node202.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html4268 HREF="node217.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html4276 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html4277 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html4275 HREF="node219.html"> Errors</A>
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<B>Up:</B> <A NAME=tex2html4273 HREF="node202.html"> File System Interface</A>
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<B> Previous:</B> <A NAME=tex2html4269 HREF="node217.html"> Loading Files</A>
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<HR> <P>
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<HR>
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<P><ADDRESS>
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AI.Repository@cs.cmu.edu
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</ADDRESS>
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</BODY>
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