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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
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<h1>luaposix 36.3</h1>
<ul>
<li><a href="../index.html">Index</a></li>
</ul>
<h2>Contents</h2>
<ul>
<li><a href="#Functions">Functions</a></li>
<li><a href="#Tables">Tables</a></li>
<li><a href="#Constants">Constants </a></li>
</ul>
<h2>Modules</h2>
<ul class="nowrap">
<li><a href="../modules/posix.html">posix</a></li>
<li><a href="../modules/posix.ctype.html">posix.ctype</a></li>
<li><a href="../modules/posix.dirent.html">posix.dirent</a></li>
<li><a href="../modules/posix.errno.html">posix.errno</a></li>
<li><strong>posix.fcntl</strong></li>
<li><a href="../modules/posix.fnmatch.html">posix.fnmatch</a></li>
<li><a href="../modules/posix.glob.html">posix.glob</a></li>
<li><a href="../modules/posix.grp.html">posix.grp</a></li>
<li><a href="../modules/posix.libgen.html">posix.libgen</a></li>
<li><a href="../modules/posix.poll.html">posix.poll</a></li>
<li><a href="../modules/posix.pwd.html">posix.pwd</a></li>
<li><a href="../modules/posix.sched.html">posix.sched</a></li>
<li><a href="../modules/posix.signal.html">posix.signal</a></li>
<li><a href="../modules/posix.stdio.html">posix.stdio</a></li>
<li><a href="../modules/posix.stdlib.html">posix.stdlib</a></li>
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<li><a href="../modules/posix.sys.resource.html">posix.sys.resource</a></li>
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<div id="content">
<h1>Module <code>posix.fcntl</code></h1>
<p>File Control.</p>
<p> Low-level control over file descriptors, including creating new file
descriptors with <code>open</code>.</p>
<h2><a href="#Functions">Functions</a></h2>
<table class="function_list">
<tr>
<td class="name" nowrap><a href="#fcntl">fcntl (fd, cmd[, arg=0])</a></td>
<td class="summary">Manipulate file descriptor.</td>
</tr>
<tr>
<td class="name" nowrap><a href="#open">open (path, oflags[, mode=511])</a></td>
<td class="summary">Open a file.</td>
</tr>
<tr>
<td class="name" nowrap><a href="#posix_fadvise">posix_fadvise (fd, offset, len, advice)</a></td>
<td class="summary">Instruct kernel on appropriate cache behaviour for a file or file segment.</td>
</tr>
</table>
<h2><a href="#Tables">Tables</a></h2>
<table class="function_list">
<tr>
<td class="name" nowrap><a href="#flock">flock</a></td>
<td class="summary">Advisory file locks.</td>
</tr>
</table>
<h2><a href="#Constants">Constants </a></h2>
<table class="function_list">
<tr>
<td class="name" nowrap><a href="#posix.fcntl">posix.fcntl</a></td>
<td class="summary">Fcntl constants.</td>
</tr>
</table>
<br/>
<br/>
<h2 class="section-header "><a name="Functions"></a>Functions</h2>
<dl class="function">
<dt>
<a name = "fcntl"></a>
<strong>fcntl (fd, cmd[, arg=0])</strong>
</dt>
<dd>
Manipulate file descriptor.
<h3>Parameters:</h3>
<ul>
<li><span class="parameter">fd</span>
<span class="types"><span class="type">int</span></span>
file descriptor to act on
</li>
<li><span class="parameter">cmd</span>
<span class="types"><span class="type">int</span></span>
operation to perform
</li>
<li><span class="parameter">arg</span>
<span class="types"><span class="type">int</span> or <a class="type" href="../modules/posix.fcntl.html#flock">flock</a></span>
when <em>cmd</em> is <code>F_GETLK</code>, <code>F_SETLK</code> or <code>F_SETLKW</code>,
then <em>arg</em> is a <a href="../modules/posix.fcntl.html#flock">flock</a> table, otherwise an integer with meaning dependent
upon the value of <em>cmd</em>.
(<em>default</em> 0)
</li>
</ul>
<h3>Returns:</h3>
<ol>
integer return value depending on <em>cmd</em>, if successful
</ol>
<h3>Or</h3>
<ol>
<li>
nil</li>
<li>
<span class="types"><a class="type" href="https://www.lua.org/manual/5.4/manual.html#6.4">string</a></span>
error message</li>
<li>
<span class="types"><span class="type">int</span></span>
errnum</li>
</ol>
<h3>See also:</h3>
<ul>
<li><a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/fcntl.html">fcntl(2)</a></li>
<li><a href="../examples/lock.lua.html#">lock.lua</a></li>
</ul>
<h3>Usage:</h3>
<ul>
<pre class="example"><span class="keyword">local</span> flag = posix.<span class="function-name">fcntl</span> (fd, posix.F_GETFL)</pre>
</ul>
</dd>
<dt>
<a name = "open"></a>
<strong>open (path, oflags[, mode=511])</strong>
</dt>
<dd>
Open a file.
<h3>Parameters:</h3>
<ul>
<li><span class="parameter">path</span>
<span class="types"><a class="type" href="https://www.lua.org/manual/5.4/manual.html#6.4">string</a></span>
</li>
<li><span class="parameter">oflags</span>
<span class="types"><span class="type">int</span></span>
bitwise OR of zero or more of <code>O_RDONLY</code>, <code>O_WRONLY</code>, <code>O_RDWR</code>,
<code>O_APPEND</code>, <code>O_CREAT</code>, <code>O_DSYNC</code>, <code>O_EXCL</code>, <code>O_NOCTTY</code>, <code>O_NONBLOCK</code>,
<code>O_RSYNC</code>, <code>O_SYNC</code> and <code>O_TRUNC</code> (and <code>O_CLOEXEC</code>, where supported)
</li>
<li><span class="parameter">mode</span>
<span class="types"><span class="type">int</span></span>
access modes used by <code>O_CREAT</code>
(<em>default</em> 511)
</li>
</ul>
<h3>Returns:</h3>
<ol>
<span class="types"><span class="type">int</span></span>
file descriptor for <em>path</em>, if successful
</ol>
<h3>Or</h3>
<ol>
<li>
nil</li>
<li>
<span class="types"><a class="type" href="https://www.lua.org/manual/5.4/manual.html#6.4">string</a></span>
error message</li>
<li>
<span class="types"><span class="type">int</span></span>
errnum</li>
</ol>
<h3>See also:</h3>
<ul>
<a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html">open(2)</a>
</ul>
<h3>Usage:</h3>
<ul>
<pre class="example"><span class="keyword">local</span> P = <span class="global">require</span> <span class="string">"posix.fcntl"</span>
fd = P.<span class="function-name">open</span> (<span class="string">"data"</span>, bit.<span class="function-name">bor</span> (P.O_CREAT, P.O_RDWR), bit.<span class="function-name">bor</span> (P.S_IRWXU, P.S_IRGRP))</pre>
</ul>
</dd>
<dt>
<a name = "posix_fadvise"></a>
<strong>posix_fadvise (fd, offset, len, advice)</strong>
</dt>
<dd>
Instruct kernel on appropriate cache behaviour for a file or file segment.
<h3>Parameters:</h3>
<ul>
<li><span class="parameter">fd</span>
<span class="types"><span class="type">int</span></span>
open file descriptor
</li>
<li><span class="parameter">offset</span>
<span class="types"><span class="type">int</span></span>
start of region
</li>
<li><span class="parameter">len</span>
<span class="types"><span class="type">int</span></span>
number of bytes in region
</li>
<li><span class="parameter">advice</span>
<span class="types"><span class="type">int</span></span>
one of <code>POSIX_FADV_NORMAL</code>, <code>POSIX_FADV_SEQUENTIAL</code>,
<code>POSIX_FADV_RANDOM</code>, <code>POSIX_FADV_NOREUSE</code>, <code>POSIX_FADV_WILLNEED</code> or
<code>POSIX_FADV_DONTNEED</code>
</li>
</ul>
<h3>Returns:</h3>
<ol>
<span class="types"><span class="type">int</span></span>
<code>0</code>, if successful
</ol>
<h3>Or</h3>
<ol>
<li>
nil</li>
<li>
<span class="types"><a class="type" href="https://www.lua.org/manual/5.4/manual.html#6.4">string</a></span>
error message</li>
<li>
<span class="types"><span class="type">int</span></span>
errnum</li>
</ol>
<h3>See also:</h3>
<ul>
<a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/posix_fadvise.html">posix_fadvise(2)</a>
</ul>
</dd>
</dl>
<h2 class="section-header "><a name="Tables"></a>Tables</h2>
<dl class="function">
<dt>
<a name = "flock"></a>
<strong>flock</strong>
</dt>
<dd>
Advisory file locks.
Passed as <em>arg</em> to <a href="../modules/posix.fcntl.html">fcntl</a> when <em>cmd</em> is <code>F_GETLK</code>, <code>F_SETLK</code> or <code>F_SETLKW</code>.
<h3>Fields:</h3>
<ul>
<li><span class="parameter">l_start</span>
<span class="types"><span class="type">int</span></span>
starting offset
</li>
<li><span class="parameter">l_len</span>
<span class="types"><span class="type">int</span></span>
len = 0 means until end of file
</li>
<li><span class="parameter">l_pid</span>
<span class="types"><span class="type">int</span></span>
lock owner
</li>
<li><span class="parameter">l_type</span>
<span class="types"><span class="type">int</span></span>
lock type
</li>
<li><span class="parameter">l_whence</span>
<span class="types"><span class="type">int</span></span>
one of <code>SEEK_SET</code>, <code>SEEK_CUR</code> or <code>SEEK_END</code>
</li>
</ul>
</dd>
</dl>
<h2 class="section-header "><a name="Constants"></a>Constants </h2>
<dl class="function">
<dt>
<a name = "posix.fcntl"></a>
<strong>posix.fcntl</strong>
</dt>
<dd>
Fcntl constants.
Any constants not available in the underlying system will be <code>0</code> valued,
if they are usually bitwise ORed with other values, otherwise <code>nil</code>.
<h3>Fields:</h3>
<ul>
<li><span class="parameter">AT_EACCESS</span>
<span class="types"><span class="type">int</span></span>
test access permitted for effective IDs, not real IDs
</li>
<li><span class="parameter">AT_FDCWD</span>
<span class="types"><span class="type">int</span></span>
indicate *at functions to use current directory
</li>
<li><span class="parameter">AT_REMOVEDIR</span>
<span class="types"><span class="type">int</span></span>
remove directory instead of unlinking file
</li>
<li><span class="parameter">AT_SYMLINK_FOLLOW</span>
<span class="types"><span class="type">int</span></span>
follow symbolic links
</li>
<li><span class="parameter">AT_SYMLINK_NOFOLLOW</span>
<span class="types"><span class="type">int</span></span>
do not follow symbolic links
</li>
<li><span class="parameter">FD_CLOEXEC</span>
<span class="types"><span class="type">int</span></span>
close file descriptor on exec flag
</li>
<li><span class="parameter">F_DUPFD</span>
<span class="types"><span class="type">int</span></span>
duplicate file descriptor
</li>
<li><span class="parameter">F_GETFD</span>
<span class="types"><span class="type">int</span></span>
get file descriptor flags
</li>
<li><span class="parameter">F_SETFD</span>
<span class="types"><span class="type">int</span></span>
set file descriptor flags
</li>
<li><span class="parameter">F_GETFL</span>
<span class="types"><span class="type">int</span></span>
get file status flags
</li>
<li><span class="parameter">F_SETFL</span>
<span class="types"><span class="type">int</span></span>
set file status flags
</li>
<li><span class="parameter">F_GETLK</span>
<span class="types"><span class="type">int</span></span>
get record locking information
</li>
<li><span class="parameter">F_SETLK</span>
<span class="types"><span class="type">int</span></span>
set record locking information
</li>
<li><span class="parameter">F_SETLKW</span>
<span class="types"><span class="type">int</span></span>
set lock, and wait if blocked
</li>
<li><span class="parameter">F_GETOWN</span>
<span class="types"><span class="type">int</span></span>
get SIGIO/SIGURG process owner
</li>
<li><span class="parameter">F_SETOWN</span>
<span class="types"><span class="type">int</span></span>
set SIGIO/SIGURG process owner
</li>
<li><span class="parameter">F_RDLCK</span>
<span class="types"><span class="type">int</span></span>
shared or read lock
</li>
<li><span class="parameter">F_WRLCK</span>
<span class="types"><span class="type">int</span></span>
exclusive or write lock
</li>
<li><span class="parameter">F_UNLCK</span>
<span class="types"><span class="type">int</span></span>
unlock
</li>
<li><span class="parameter">O_RDONLY</span>
<span class="types"><span class="type">int</span></span>
open for reading only
</li>
<li><span class="parameter">O_WRONLY</span>
<span class="types"><span class="type">int</span></span>
open for writing only
</li>
<li><span class="parameter">O_RDWR</span>
<span class="types"><span class="type">int</span></span>
open for reading and writing
</li>
<li><span class="parameter">O_APPEND</span>
<span class="types"><span class="type">int</span></span>
set append mode
</li>
<li><span class="parameter">O_CLOEXEC</span>
<span class="types"><span class="type">int</span></span>
set FD_CLOEXEC atomically
</li>
<li><span class="parameter">O_CREAT</span>
<span class="types"><span class="type">int</span></span>
create if nonexistent
</li>
<li><span class="parameter">O_DSYNC</span>
<span class="types"><span class="type">int</span></span>
synchronise io data integrity
</li>
<li><span class="parameter">O_EXCL</span>
<span class="types"><span class="type">int</span></span>
error if file already exists
</li>
<li><span class="parameter">O_NOCTTY</span>
<span class="types"><span class="type">int</span></span>
don't assign controlling terminal
</li>
<li><span class="parameter">O_NONBLOCK</span>
<span class="types"><span class="type">int</span></span>
no delay
</li>
<li><span class="parameter">O_RSYNC</span>
<span class="types"><span class="type">int</span></span>
synchronise file read integrity
</li>
<li><span class="parameter">O_SYNC</span>
<span class="types"><span class="type">int</span></span>
synchronise file write integrity
</li>
<li><span class="parameter">O_TRUNC</span>
<span class="types"><span class="type">int</span></span>
truncate to zero length
</li>
<li><span class="parameter">POSIX_FADV_NORMAL</span>
<span class="types"><span class="type">int</span></span>
no advice
</li>
<li><span class="parameter">POSIX_FADV_SEQUENTIAL</span>
<span class="types"><span class="type">int</span></span>
expecting to access data sequentially
</li>
<li><span class="parameter">POSIX_FADV_RANDOM</span>
<span class="types"><span class="type">int</span></span>
expecting to access data randomly
</li>
<li><span class="parameter">POSIX_FADV_NOREUSE</span>
<span class="types"><span class="type">int</span></span>
expecting to access data once only
</li>
<li><span class="parameter">POSIX_FADV_WILLNEED</span>
<span class="types"><span class="type">int</span></span>
expecting to access data in the near future
</li>
<li><span class="parameter">POSIX_FADV_DONTNEED</span>
<span class="types"><span class="type">int</span></span>
not expecting to access the data in the near future
</li>
</ul>
<h3>Usage:</h3>
<ul>
<pre class="example"><span class="comment">-- Print fcntl constants supported on this host.
</span><span class="keyword">for</span> name, value <span class="keyword">in</span> <span class="global">pairs</span> (<span class="global">require</span> <span class="string">"posix.fcntl"</span>) <span class="keyword">do</span>
<span class="keyword">if</span> <span class="global">type</span> (value) == <span class="string">"number"</span> <span class="keyword">then</span>
<span class="global">print</span> (name, value)
<span class="keyword">end</span>
<span class="keyword">end</span></pre>
</ul>
</dd>
</dl>
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