xbd_chap03.html

IEEE 1003.1-2003, Single Unix Specification v3

Expression using a more extensive syntax, occasionally used by some utilities. <basefont size="2"></p>

<dl>
<dt><b>Note:</b></dt>

<dd>Extended Regular Expressions are described in detail in <a href="xbd_chap09.html#tag_09_04"><i>Extended Regular
Expressions</i></a> .</dd>
</dl>

<basefont size="3"> 

<h3><a name="tag_03_159"></a>Extended Security Controls</h3>

<p>Implementation-defined security controls allowed by the file access permission and appropriate privilege (see also <a href=
"#tag_03_19">Appropriate Privileges</a> ) mechanisms, through which an implementation can support different security policies from
those described in IEEE&nbsp;Std&nbsp;1003.1-2001. <basefont size="2"></p>

<dl>
<dt><b>Note:</b></dt>

<dd>See also Extended Security Controls defined in <a href="xbd_chap04.html#tag_04_03"><i>Extended Security Controls</i></a> . 

<p>File Access Permissions are defined in detail in <a href="xbd_chap04.html#tag_04_04"><i>File Access Permissions</i></a> .</p>
</dd>
</dl>

<basefont size="3"> 

<h3><a name="tag_03_160"></a>Feature Test Macro</h3>

<p>A macro used to determine whether a particular set of features is included from a header. <basefont size="2"></p>

<dl>
<dt><b>Note:</b></dt>

<dd>See also the System Interfaces volume of IEEE&nbsp;Std&nbsp;1003.1-2001, <a href="../functions/xsh_chap02_02.html">Section 2.2,
The Compilation Environment</a>.</dd>
</dl>

<basefont size="3"> 

<h3><a name="tag_03_161"></a>Field</h3>

<p>In the shell command language, a unit of text that is the result of parameter expansion, arithmetic expansion, command
substitution, or field splitting. During command processing, the resulting fields are used as the command name and its arguments.
<basefont size="2"></p>

<dl>
<dt><b>Note:</b></dt>

<dd>Parameter Expansion is defined in detail in the Shell and Utilities volume of IEEE&nbsp;Std&nbsp;1003.1-2001, <a href=
"../utilities/xcu_chap02.html#tag_02_06_02">Section 2.6.2, Parameter Expansion</a>. 

<p>Arithmetic Expansion is defined in detail in the Shell and Utilities volume of IEEE&nbsp;Std&nbsp;1003.1-2001, <a href=
"../utilities/xcu_chap02.html#tag_02_06_04">Section 2.6.4, Arithmetic Expansion</a>.</p>

<p>Command Substitution is defined in detail in the Shell and Utilities volume of IEEE&nbsp;Std&nbsp;1003.1-2001, <a href=
"../utilities/xcu_chap02.html#tag_02_06_03">Section 2.6.3, Command Substitution</a>.</p>

<p>Field Splitting is defined in detail in the Shell and Utilities volume of IEEE&nbsp;Std&nbsp;1003.1-2001, <a href=
"../utilities/xcu_chap02.html#tag_02_06_05">Section 2.6.5, Field Splitting</a>.</p>

<p>For further information on command processing, see the Shell and Utilities volume of IEEE&nbsp;Std&nbsp;1003.1-2001, <a href=
"../utilities/xcu_chap02.html#tag_02_09_01">Section 2.9.1, Simple Commands</a>.</p>
</dd>
</dl>

<basefont size="3"> 

<h3><a name="tag_03_162"></a>FIFO Special File (or FIFO)</h3>

<p>A type of file with the property that data written to such a file is read on a first-in-first-out basis. <basefont size="2"></p>

<dl>
<dt><b>Note:</b></dt>

<dd>Other characteristics of FIFOs are described in the System Interfaces volume of IEEE&nbsp;Std&nbsp;1003.1-2001, <a href=
"../functions/lseek.html"><i>lseek</i>()</a>, <a href="../functions/open.html"><i>open</i>()</a>, <a href=
"../functions/read.html"><i>read</i>()</a>, and <a href="../functions/write.html"><i>write</i>()</a>.</dd>
</dl>

<basefont size="3"> 

<h3><a name="tag_03_163"></a>File</h3>

<p>An object that can be written to, or read from, or both. A file has certain attributes, including access permissions and type.
File types include regular file, character special file, block special file, FIFO special file, symbolic link, socket, and
directory. Other types of files may be supported by the implementation.</p>

<h3><a name="tag_03_164"></a>File Description</h3>

<p>See <i>Open File Description</i> in <a href="#tag_03_253">Open File Description</a> .</p>

<h3><a name="tag_03_165"></a>File Descriptor</h3>

<p>A per-process unique, non-negative integer used to identify an open file for the purpose of file access. The value of a file
descriptor is from zero to {OPEN_MAX}. A process can have no more than {OPEN_MAX} file descriptors open simultaneously. File
descriptors may also be used to implement message catalog descriptors and directory streams; see also <a href="#tag_03_253">Open
File Description</a> . <basefont size="2"></p>

<dl>
<dt><b>Note:</b></dt>

<dd>{OPEN_MAX} is defined in detail in <a href="limits.h.html"><i>&lt;limits.h&gt;</i></a> .</dd>
</dl>

<basefont size="3"> 

<h3><a name="tag_03_166"></a>File Group Class</h3>

<p>The property of a file indicating access permissions for a process related to the group identification of a process. A process
is in the file group class of a file if the process is not in the file owner class and if the effective group ID or one of the
supplementary group IDs of the process matches the group ID associated with the file. Other members of the class may be
implementation-defined.</p>

<h3><a name="tag_03_167"></a>File Mode</h3>

<p>An object containing the file mode bits and file type of a file. <basefont size="2"></p>

<dl>
<dt><b>Note:</b></dt>

<dd>File mode bits and file types are defined in detail in <a href="sys/stat.h.html"><i>&lt;sys/stat.h&gt;</i></a> .</dd>
</dl>

<basefont size="3"> 

<h3><a name="tag_03_168"></a>File Mode Bits</h3>

<p>A file's file permission bits: set-user-ID-on-execution bit (S_ISUID), set-group-ID-on-execution bit (S_ISGID), and, on
directories, the restricted deletion flag bit (S_ISVTX). <basefont size="2"></p>

<dl>
<dt><b>Note:</b></dt>

<dd>File Mode Bits are defined in detail in <a href="sys/stat.h.html"><i>&lt;sys/stat.h&gt;</i></a> .</dd>
</dl>

<basefont size="3"> 

<h3><a name="tag_03_169"></a>Filename</h3>

<p>A name consisting of 1 to {NAME_MAX} bytes used to name a file. The characters composing the name may be selected from the set
of all character values excluding the slash character and the null byte. The filenames dot and dot-dot have special meaning. A
filename is sometimes referred to as a &quot;pathname component&quot;. <basefont size="2"></p>

<dl>
<dt><b>Note:</b></dt>

<dd>Pathname Resolution is defined in detail in <a href="xbd_chap04.html#tag_04_11"><i>Pathname Resolution</i></a> .</dd>
</dl>

<basefont size="3"> 

<h3><a name="tag_03_170"></a>Filename Portability</h3>

<p>Filenames should be constructed from the portable filename character set because the use of other characters can be confusing or
ambiguous in certain contexts. (For example, the use of a colon ( <tt>':'</tt> ) in a pathname could cause ambiguity if that
pathname were included in a <i>PATH</i> definition.)</p>

<h3><a name="tag_03_171"></a>File Offset</h3>

<p>The byte position in the file where the next I/O operation begins. Each open file description associated with a regular file,
block special file, or directory has a file offset. A character special file that does not refer to a terminal device may have a
file offset. There is no file offset specified for a pipe or FIFO.</p>

<h3><a name="tag_03_172"></a>File Other Class</h3>

<p>The property of a file indicating access permissions for a process related to the user and group identification of a process. A
process is in the file other class of a file if the process is not in the file owner class or file group class.</p>

<h3><a name="tag_03_173"></a>File Owner Class</h3>

<p>The property of a file indicating access permissions for a process related to the user identification of a process. A process is
in the file owner class of a file if the effective user ID of the process matches the user ID of the file.</p>

<h3><a name="tag_03_174"></a>File Permission Bits</h3>

<p>Information about a file that is used, along with other information, to determine whether a process has read, write, or
execute/search permission to a file. The bits are divided into three parts: owner, group, and other. Each part is used with the
corresponding file class of processes. These bits are contained in the file mode. <basefont size="2"></p>

<dl>
<dt><b>Note:</b></dt>

<dd>File modes are defined in detail in <a href="sys/stat.h.html"><i>&lt;sys/stat.h&gt;</i></a> . 

<p>File Access Permissions are defined in detail in <a href="xbd_chap04.html#tag_04_04"><i>File Access Permissions</i></a> .</p>
</dd>
</dl>

<basefont size="3"> 

<h3><a name="tag_03_175"></a>File Serial Number</h3>

<p>A per-file system unique identifier for a file.</p>

<h3><a name="tag_03_176"></a>File System</h3>

<p>A collection of files and certain of their attributes. It provides a name space for file serial numbers referring to those
files.</p>

<h3><a name="tag_03_177"></a>File Type</h3>

<p>See <i>File</i> in <a href="#tag_03_163">File</a> .</p>

<h3><a name="tag_03_178"></a>Filter</h3>

<p>A command whose operation consists of reading data from standard input or a list of input files and writing data to standard
output. Typically, its function is to perform some transformation on the data stream.</p>

<h3><a name="tag_03_179"></a>First Open (of a File)</h3>

<p>When a process opens a file that is not currently an open file within any process.</p>

<h3><a name="tag_03_180"></a>Flow Control</h3>

<p>The mechanism employed by a communications provider that constrains a sending entity to wait until the receiving entities can
safely receive additional data without loss.</p>

<h3><a name="tag_03_181"></a>Foreground Job</h3>

<p>See <i>Foreground Process Group</i> in <a href="#tag_03_183">Foreground Process Group (or Foreground Job)</a> .</p>

<h3><a name="tag_03_182"></a>Foreground Process</h3>

<p>A process that is a member of a foreground process group.</p>

<h3><a name="tag_03_183"></a>Foreground Process Group (or Foreground Job)</h3>

<p>A process group whose member processes have certain privileges, denied to processes in background process groups, when accessing
their controlling terminal. Each session that has established a connection with a controlling terminal has at most one process
group of the session as the foreground process group of that controlling terminal. <basefont size="2"></p>

<dl>
<dt><b>Note:</b></dt>

<dd>The General Terminal Interface is defined in detail in <a href="xbd_chap11.html#tag_11"><i>General Terminal Interface</i></a>
.</dd>
</dl>

<basefont size="3"> 

<h3><a name="tag_03_184"></a>Foreground Process Group ID</h3>

<p>The process group ID of the foreground process group.</p>

<h3><a name="tag_03_185"></a>Form-Feed Character (&lt;form-feed&gt;)</h3>

<p>A character that in the output stream indicates that printing should start on the next page of an output device. It is the
character designated by <tt>'\f'</tt> in the C language. If the &lt;form-feed&gt; is not the first character of an output line, the
result is unspecified. It is unspecified whether this character is the exact sequence transmitted to an output device by the system
to accomplish the movement to the next page.</p>

<h3><a name="tag_03_186"></a>Graphic Character</h3>

<p>A member of the <b>graph</b> character class of the current locale. <basefont size="2"></p>

<dl>
<dt><b>Note:</b></dt>

<dd>The <b>graph</b> character class is defined in detail in <a href="xbd_chap07.html#tag_07_03_01"><i>LC_CTYPE</i></a> .</dd>
</dl>

<basefont size="3"> 

<h3><a name="tag_03_187"></a>Group Database</h3>

<p>A system database of implementation-defined format that contains at least the following information for each group ID:</p>

<ul>
<li>
<p>Group name</p>
</li>

<li>
<p>Numerical group ID</p>
</li>

<li>
<p>List of users allowed in the group</p>
</li>
</ul>

<p>The list of users allowed in the group is used by the <a href="../utilities/newgrp.html"><i>newgrp</i></a> utility. <basefont
size="2"></p>

<dl>
<dt><b>Note:</b></dt>

<dd>The <a href="../utilities/newgrp.html"><i>newgrp</i></a> utility is defined in detail in the Shell and Utilities volume of
IEEE&nbsp;Std&nbsp;1003.1-2001.</dd>
</dl>

<basefont size="3"> 

<h3><a name="tag_03_188"></a>Group ID</h3>

<p>A non-negative integer, which can be contained in an object of type <b>gid_t</b>, that is used to identify a group of system
users. Each system user is a member of at least one group. When the identity of a group is associated with a process, a group ID
value is referred to as a real group ID, an effective group ID, one of the supplementary group IDs, or a saved set-group-ID.</p>

<h3><a name="tag_03_189"></a>Group Name</h3>

<p>A string that is used to identify a group; see also <a href="#tag_03_187">Group Database</a> . To be portable across conforming
systems, the value is composed of characters from the portable filename character set. The hyphen should not be used as the first
character of a portable group name.</p>

<h3><a name="tag_03_190"></a>Hard Limit</h3>

<p>A system resource limitation that may be reset to a lesser or greater limit by a privileged process. A non-privileged process is
restricted to only lowering its hard limit.</p>

<h3