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| <h4 class="subsection">11.2.2 File Name Resolution</h4> |
| |
| <p>A file name consists of file name components separated by slash |
| (‘<samp><span class="samp">/</span></samp>’) characters. On the systems that the GNU C library supports, |
| multiple successive ‘<samp><span class="samp">/</span></samp>’ characters are equivalent to a single |
| ‘<samp><span class="samp">/</span></samp>’ character. |
| |
| <p><a name="index-file-name-resolution-908"></a>The process of determining what file a file name refers to is called |
| <dfn>file name resolution</dfn>. This is performed by examining the |
| components that make up a file name in left-to-right order, and locating |
| each successive component in the directory named by the previous |
| component. Of course, each of the files that are referenced as |
| directories must actually exist, be directories instead of regular |
| files, and have the appropriate permissions to be accessible by the |
| process; otherwise the file name resolution fails. |
| |
| <p><a name="index-root-directory-909"></a><a name="index-absolute-file-name-910"></a>If a file name begins with a ‘<samp><span class="samp">/</span></samp>’, the first component in the file |
| name is located in the <dfn>root directory</dfn> of the process (usually all |
| processes on the system have the same root directory). Such a file name |
| is called an <dfn>absolute file name</dfn>. |
| <!-- !!! xref here to chroot, if we ever document chroot. -rm --> |
| |
| <p><a name="index-relative-file-name-911"></a>Otherwise, the first component in the file name is located in the |
| current working directory (see <a href="Working-Directory.html#Working-Directory">Working Directory</a>). This kind of |
| file name is called a <dfn>relative file name</dfn>. |
| |
| <p><a name="index-parent-directory-912"></a>The file name components <samp><span class="file">.</span></samp> (“dot”) and <samp><span class="file">..</span></samp> (“dot-dot”) |
| have special meanings. Every directory has entries for these file name |
| components. The file name component <samp><span class="file">.</span></samp> refers to the directory |
| itself, while the file name component <samp><span class="file">..</span></samp> refers to its |
| <dfn>parent directory</dfn> (the directory that contains the link for the |
| directory in question). As a special case, <samp><span class="file">..</span></samp> in the root |
| directory refers to the root directory itself, since it has no parent; |
| thus <samp><span class="file">/..</span></samp> is the same as <samp><span class="file">/</span></samp>. |
| |
| <p>Here are some examples of file names: |
| |
| <dl> |
| <dt><samp><span class="file">/a</span></samp><dd>The file named <samp><span class="file">a</span></samp>, in the root directory. |
| |
| <br><dt><samp><span class="file">/a/b</span></samp><dd>The file named <samp><span class="file">b</span></samp>, in the directory named <samp><span class="file">a</span></samp> in the root directory. |
| |
| <br><dt><samp><span class="file">a</span></samp><dd>The file named <samp><span class="file">a</span></samp>, in the current working directory. |
| |
| <br><dt><samp><span class="file">/a/./b</span></samp><dd>This is the same as <samp><span class="file">/a/b</span></samp>. |
| |
| <br><dt><samp><span class="file">./a</span></samp><dd>The file named <samp><span class="file">a</span></samp>, in the current working directory. |
| |
| <br><dt><samp><span class="file">../a</span></samp><dd>The file named <samp><span class="file">a</span></samp>, in the parent directory of the current working |
| directory. |
| </dl> |
| |
| <!-- An empty string may ``work'', but I think it's confusing to --> |
| <!-- try to describe it. It's not a useful thing for users to use-rms. --> |
| <p>A file name that names a directory may optionally end in a ‘<samp><span class="samp">/</span></samp>’. |
| You can specify a file name of <samp><span class="file">/</span></samp> to refer to the root directory, |
| but the empty string is not a meaningful file name. If you want to |
| refer to the current working directory, use a file name of <samp><span class="file">.</span></samp> or |
| <samp><span class="file">./</span></samp>. |
| |
| <p>Unlike some other operating systems, the GNU system doesn't have any |
| built-in support for file types (or extensions) or file versions as part |
| of its file name syntax. Many programs and utilities use conventions |
| for file names—for example, files containing C source code usually |
| have names suffixed with ‘<samp><span class="samp">.c</span></samp>’—but there is nothing in the file |
| system itself that enforces this kind of convention. |
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