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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
(&lsquo;<samp><span class="samp">/</span></samp>&rsquo;) characters.  On the systems that the GNU C library supports,
multiple successive &lsquo;<samp><span class="samp">/</span></samp>&rsquo; characters are equivalent to a single
&lsquo;<samp><span class="samp">/</span></samp>&rsquo; 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 &lsquo;<samp><span class="samp">/</span></samp>&rsquo;, 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> (&ldquo;dot&rdquo;) and <samp><span class="file">..</span></samp> (&ldquo;dot-dot&rdquo;)
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 &lsquo;<samp><span class="samp">/</span></samp>&rsquo;. 
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&mdash;for example, files containing C source code usually
have names suffixed with &lsquo;<samp><span class="samp">.c</span></samp>&rsquo;&mdash;but there is nothing in the file
system itself that enforces this kind of convention.

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