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Introduction</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-2/c-b-character-syntax.html">2. Syntax</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-3/d-b-evaluation.html">3. Evaluation and Compilation</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-4/e-b-introduction.html">4. Types and Classes</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-5/f-b-generalized-reference.html">5. Data and Control Flow</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-6/g-b-the-loop-facility.html">6. Iteration</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-7/h-b-object-creation-and-initialization.html">7. Objects</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../category/81-structures-dictionary.html">8. Structures</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-9/j-b-condition-system-concepts.html">9. Conditions</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-10/ba-b-symbol-concepts.html">10. Symbols</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-11/bb-b-package-concepts.html">11. Packages</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-12/bc-b-number-concepts.html">12. Numbers</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-13/bd-b-character-concepts.html">13. Characters</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-14/be-b-cons-concepts.html">14. Conses</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-15/bf-b-array-concepts.html">15. Arrays</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-16/bg-b-string-concepts.html">16. Strings</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-17/bh-b-sequence-concepts.html">17. Sequences</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-18/bi-b-hash-table-concepts.html">18. Hash Tables</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-19/bj-b-overview-of-filenames.html">19. Filenames</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret menu__link--active" aria-expanded="true" href="ca-b-file-system-concepts.html">20. Files</a></div><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link menu__link--active" aria-current="page" tabindex="0" href="ca-b-file-system-concepts.html">20.1 File System Concepts</a></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-2 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist" aria-expanded="false" tabindex="0" href="../category/202-files-dictionary.html">20.2 Files Dictionary</a><button aria-label="Expand sidebar category '20.2 Files Dictionary'" type="button" class="clean-btn menu__caret"></button></div></li></ul></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-21/cb-b-stream-concepts.html">21. Streams</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-22/cc-b-the-lisp-printer.html">22. Printer</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-23/cd-b-reader-concepts.html">23. Reader</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-24/ce-b-system-construction-concepts.html">24. System Construction</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-25/cf-b-the-external-environment.html">25. External Environment</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../environments.html">26. Environments</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../meta-object-protocol.html">27. Meta Object Protocol</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../data-structures.html">28. Data Structures</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../portability/trivial-packages.html">29. Portability</a></div></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-1 menu__list-item"><a class="menu__link" href="../dictionary-entries.html">dictionary-entries</a></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../chap-26/intro.html">Glossary</a></div></li></ul></nav></div></div></aside><main class="docMainContainer_TBSr"><div class="container padding-top--md padding-bottom--lg"><div class="row"><div class="col docItemCol_VOVn"><div class="docItemContainer_Djhp"><article><nav class="theme-doc-breadcrumbs breadcrumbsContainer_Z_bl" aria-label="Breadcrumbs"><ul class="breadcrumbs" itemscope="" itemtype="https://schema.org/BreadcrumbList"><li class="breadcrumbs__item"><a aria-label="Home page" class="breadcrumbs__link" href="../index.html"><svg viewBox="0 0 24 24" class="breadcrumbHomeIcon_YNFT"><path d="M10 19v-5h4v5c0 .55.45 1 1 1h3c.55 0 1-.45 1-1v-7h1.7c.46 0 .68-.57.33-.87L12.67 3.6c-.38-.34-.96-.34-1.34 0l-8.36 7.53c-.34.3-.13.87.33.87H5v7c0 .55.45 1 1 1h3c.55 0 1-.45 1-1z" fill="currentColor"></path></svg></a></li><li class="breadcrumbs__item"><span class="breadcrumbs__link">20. Files</span><meta itemprop="position" content="1"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item breadcrumbs__item--active"><span class="breadcrumbs__link" itemprop="name">20.1 File System Concepts</span><meta itemprop="position" content="2"></li></ul></nav><div class="tocCollapsible_ETCw theme-doc-toc-mobile tocMobile_ITEo"><button type="button" class="clean-btn tocCollapsibleButton_TO0P">On this page</button></div><div class="theme-doc-markdown markdown"><h1>20.1 File System Concepts</h1>
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<p>This section describes the Common Lisp interface to file systems. The model used by this interface assumes that <span><i>files</i></span> are named by <span><i>filenames</i></span>, that a <span><i>filename</i></span> can be represented by a <em>pathname object</em>, and that given a <span><i>pathname</i></span> a <span><i>stream</i></span> can be constructed that connects to a <span><i>file</i></span> whose <span><i>filename</i></span> it represents.</p>
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<p>For information about opening and closing <span><i>files</i></span>, and manipulating their contents, see Chapter 21 (Streams).</p>
|
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<p>Figure 20–1 lists some <span><i>operators</i></span> that are applicable to <span><i>files</i></span> and directories.</p>
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<p>|</p><p><strong>compile-file file-length open</strong> </p><p><strong>delete-file file-position probe-file</strong> </p><p><strong>directory file-write-date rename-file</strong> </p><p><strong>file-author load with-open-file</strong></p>|<p></p>
|
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<p>| :- |</p>
|
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<p><strong>Figure 20–1. File and Directory Operations</strong></p>
|
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<h2 class="anchor anchorWithStickyNavbar_LWe7" id="2011-coercion-of-streams-to-pathnames">20.1.1 Coercion of Streams to Pathnames<a href="ca-b-file-system-concepts.html#2011-coercion-of-streams-to-pathnames" class="hash-link" aria-label="Direct link to 20.1.1 Coercion of Streams to Pathnames" title="Direct link to 20.1.1 Coercion of Streams to Pathnames"></a></h2>
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<p>A <span><i>stream associated with a file</i></span> is either a <span><i>file stream</i></span> or a <span><i>synonym stream</i></span> whose target is a <span><i>stream associated with a file</i></span>. Such streams can be used as <span><i>pathname designators</i></span>.</p>
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<p>Normally, when a <span><i>stream associated with a file</i></span> is used as a <span><i>pathname designator</i></span> , it denotes the <span><i>pathname</i></span> used to open the <span><i>file</i></span>; this may be, but is not required to be, the actual name of the <span><i>file</i></span>.</p>
|
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<p>Some functions, such as <span><b>truename</b></span> and <span><b>delete-file</b></span>, coerce <span><i>streams</i></span> to <span><i>pathnames</i></span> in a different way that involves referring to the actual <span><i>file</i></span> that is open, which might or might not be the file whose name was opened originally. Such special situations are always notated specifically and are not the default.</p>
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<h2 class="anchor anchorWithStickyNavbar_LWe7" id="2012-file-operations-on-open-and-closed-streams">20.1.2 File Operations on Open and Closed Streams<a href="ca-b-file-system-concepts.html#2012-file-operations-on-open-and-closed-streams" class="hash-link" aria-label="Direct link to 20.1.2 File Operations on Open and Closed Streams" title="Direct link to 20.1.2 File Operations on Open and Closed Streams"></a></h2>
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<p>Many <span><i>functions</i></span> that perform <span><i>file</i></span> operations accept either <span><i>open</i></span> or <em>closed streams</em> as <span><i>arguments</i></span>; see Section 21.1.3 (Stream Arguments to Standardized Functions).</p>
|
||
<p>Of these, the <span><i>functions</i></span> in Figure 20–2 treat <span><i>open</i></span> and <em>closed streams</em> differently.</p>
|
||
<p>|</p><p><strong>delete-file file-author probe-file</strong> </p><p><strong>directory file-write-date truename</strong></p>|<p></p>
|
||
<p>| :- |</p>
|
||
<p><strong>Figure 20–2. File Functions that Treat Open and Closed Streams Differently</strong></p>
|
||
<p>Since treatment of <em>open streams</em> by the <span><i>file system</i></span> may vary considerably between <span><i>implementations</i></span>, however, a <em>closed stream</em> might be the most reliable kind of <span><i>argument</i></span> for some of these functions—in particular, those in Figure 20–3. For example, in some <span><i>file systems</i></span>, <em>open files</em> are written under temporary names and not renamed until <span><i>closed</i></span> and/or are held invisible until <span><i>closed</i></span>. In general, any code that is intended to be portable should use such <span><i>functions</i></span> carefully.</p>
|
||
<p>|<strong>directory probe-file truename</strong>|</p>
|
||
<p>| :- |</p>
|
||
<p><strong>Figure 20–3. File Functions where Closed Streams Might Work Best</strong></p>
|
||
<h2 class="anchor anchorWithStickyNavbar_LWe7" id="2013-truenames">20.1.3 Truenames<a href="ca-b-file-system-concepts.html#2013-truenames" class="hash-link" aria-label="Direct link to 20.1.3 Truenames" title="Direct link to 20.1.3 Truenames"></a></h2>
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<p>Many <span><i>file systems</i></span> permit more than one <span><i>filename</i></span> to designate a particular <span><i>file</i></span>.</p>
|
||
<p>Even where multiple names are possible, most <span><i>file systems</i></span> have a convention for generating a canonical <span><i>filename</i></span> in such situations. Such a canonical <span><i>filename</i></span> (or the <span><i>pathname</i></span> representing such a <span><i>filename</i></span>) is called a <span><i>truename</i></span>.</p>
|
||
<p>The <span><i>truename</i></span> of a <span><i>file</i></span> may differ from other <span><i>filenames</i></span> for the file because of symbolic links, version numbers, logical device translations in the <span><i>file system</i></span>, <span><i>logical pathname</i></span> translations within Common Lisp, or other artifacts of the <span><i>file system</i></span>.</p>
|
||
<p>The <span><i>truename</i></span> for a <span><i>file</i></span> is often, but not necessarily, unique for each <span><i>file</i></span>. For instance, a Unix <span><i>file</i></span> with multiple hard links could have several <span><i>truenames</i></span>.</p>
|
||
<h3 class="anchor anchorWithStickyNavbar_LWe7" id="20131-examples-of-truenames">20.1.3.1 Examples of Truenames<a href="ca-b-file-system-concepts.html#20131-examples-of-truenames" class="hash-link" aria-label="Direct link to 20.1.3.1 Examples of Truenames" title="Direct link to 20.1.3.1 Examples of Truenames"></a></h3>
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<p>For example, a DEC TOPS-20 system with <span><i>files</i></span> PS:<JOE>FOO.TXT.1 and PS:<JOE>FOO.TXT.2 might permit the second <span><i>file</i></span> to be referred to as PS:<JOE>FOO.TXT.0, since the “.0” notation denotes “newest” version of several <span><i>files</i></span>. In the same <span><i>file system</i></span>, a “logical device” “JOE:” might be taken to refer to PS:<JOE>” and so the names JOE<!-- -->:FOO<!-- -->.TXT.2 or JOE<!-- -->:FOO<!-- -->.TXT.0 might refer to PS:<JOE>FOO.TXT.2. In all of these cases, the <span><i>truename</i></span> of the file would probably be PS:<JOE>FOO.TXT.2.</p>
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<p>If a <span><i>file</i></span> is a symbolic link to another <span><i>file</i></span> (in a <span><i>file system</i></span> permitting such a thing), it is conventional for the <span><i>truename</i></span> to be the canonical name of the <span><i>file</i></span> after any symbolic links have been followed; that is, it is the canonical name of the <span><i>file</i></span> whose contents would become available if an <em>input stream</em> to that <span><i>file</i></span> were opened.</p>
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<p>In the case of a <span><i>file</i></span> still being created (that is, of an <em>output stream</em> open to such a <span><i>file</i></span>), the exact <span><i>truename</i></span> of the file might not be known until the <span><i>stream</i></span> is closed. In this case, the <span><i>function</i></span> <span><b>truename</b></span> might return different values for such a <span><i>stream</i></span> before and after it was closed. In fact, before it is closed, the name returned might not even be a valid name in the <span><i>file system</i></span>—for example, while a file is being written, it might have version <!-- -->:newest<!-- --> and might only take on a specific numeric value later when the file is closed even in a <span><i>file system</i></span> where all files have numeric versions.</p></div><footer class="theme-doc-footer docusaurus-mt-lg"><div class="theme-doc-footer-edit-meta-row row"><div class="col"><a href="https://github.com/lisp-docs/cl-language-reference/tree/main/docs/chap-20/ca-b-file-system-concepts.md" target="_blank" rel="noopener noreferrer" class="theme-edit-this-page"><svg fill="currentColor" height="20" width="20" viewBox="0 0 40 40" class="iconEdit_Z9Sw" aria-hidden="true"><g><path d="m34.5 11.7l-3 3.1-6.3-6.3 3.1-3q0.5-0.5 1.2-0.5t1.1 0.5l3.9 3.9q0.5 0.4 0.5 1.1t-0.5 1.2z m-29.5 17.1l18.4-18.5 6.3 6.3-18.4 18.4h-6.3v-6.2z"></path></g></svg>Edit this page</a></div><div class="col 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