lp.html

IEEE 1003.1-2003, Single Unix Specification v3

<blockquote>
<p>The following exit values shall be returned:</p>

<dl compact>
<dt>&nbsp;0</dt>

<dd>All input files were processed successfully.</dd>

<dt>&gt;0</dt>

<dd>No output device was available, or an error occurred.</dd>
</dl>
</blockquote>

<h4><a name="tag_04_80_15"></a>CONSEQUENCES OF ERRORS</h4>

<blockquote>
<p>Default.</p>
</blockquote>

<hr>
<div class="box"><em>The following sections are informative.</em></div>

<h4><a name="tag_04_80_16"></a>APPLICATION USAGE</h4>

<blockquote>
<p>The <a href="../utilities/pr.html"><i>pr</i></a> and <a href="../utilities/fold.html"><i>fold</i></a> utilities can be used to
achieve reasonable formatting for the implementation's default page size.</p>

<p>A conforming application can use one of the <i>file</i> operands only with the <b>-c</b> option or if the file is publicly
readable and guaranteed to be available at the time of printing. This is because IEEE&nbsp;Std&nbsp;1003.1-2001 gives the
implementation the freedom to queue up the request for printing at some later time by a different process that might not be able to
access the file.</p>
</blockquote>

<h4><a name="tag_04_80_17"></a>EXAMPLES</h4>

<blockquote>
<ol>
<li>
<p>To print file <i>file</i>:</p>

<pre>
<tt>lp -c</tt> <i>file</i>
</pre>
</li>

<li>
<p>To print multiple files with headers:</p>

<pre>
<tt>pr</tt> <i>file1 file2</i> <tt>| lp
</tt>
</pre>
</li>
</ol>
</blockquote>

<h4><a name="tag_04_80_18"></a>RATIONALE</h4>

<blockquote>
<p>The <i>lp</i> utility was designed to be a basic version of a utility that is already available in many historical
implementations. The standard developers considered that it should be implementable simply as:</p>

<pre>
<tt>cat "$@" &gt; /dev/lp
</tt>
</pre>

<p>after appropriate processing of options, if that is how the implementation chose to do it and if exclusive access could be
granted (so that two users did not write to the device simultaneously). Although in the future the standard developers may add
other options to this utility, it should always be able to execute with no options or operands and send the standard input to an
unspecified output device.</p>

<p>This volume of IEEE&nbsp;Std&nbsp;1003.1-2001 makes no representations concerning the format of the printed output, except that
it must be &quot;human-readable&quot; and &quot;non-volatile&quot;. Thus, writing by default to a disk or tape drive or a display terminal would
not qualify. (Such destinations are not prohibited when <b>-d</b> <i>dest</i>, <i>LPDEST ,</i> or <i>PRINTER</i> are used,
however.)</p>

<p>This volume of IEEE&nbsp;Std&nbsp;1003.1-2001 is worded such that a &quot;print job&quot; consisting of multiple input files, possibly
in multiple copies, is guaranteed to print so that any one file is not intermixed with another, but there is no statement that all
the files or copies have to print out together.</p>

<p>The <b>-c</b> option may imply a spooling operation, but this is not required. The utility can be implemented to wait until the
printer is ready and then wait until it is finished. Because of that, there is no attempt to define a queuing mechanism
(priorities, classes of output, and so on).</p>

<p>On some historical systems, the request ID reported on the STDOUT can be used to later cancel or find the status of a request
using utilities not defined in this volume of IEEE&nbsp;Std&nbsp;1003.1-2001.</p>

<p>Although the historical System V <i>lp</i> and BSD <i>lpr</i> utilities have provided similar functionality, they used different
names for the environment variable specifying the destination printer. Since the name of the utility here is <i>lp</i>,
<i>LPDEST</i> (used by the System V <i>lp</i> utility) was given precedence over <i>PRINTER</i> (used by the BSD <i>lpr</i>
utility). Since environments of users frequently contain one or the other environment variable, the <i>lp</i> utility is required
to recognize both. If this was not done, many applications would send output to unexpected output devices when users moved from
system to system.</p>

<p>Some have commented that <i>lp</i> has far too little functionality to make it worthwhile. Requests have proposed additional
options or operands or both that added functionality. The requests included:</p>

<ul>
<li>
<p>Wording <i>requiring</i> the output to be &quot;hardcopy&quot;</p>
</li>

<li>
<p>A requirement for multiple printers</p>
</li>

<li>
<p>Options for supporting various page-description languages</p>
</li>
</ul>

<p>Given that a compliant system is not required to even have a printer, placing further restrictions upon the behavior of the
printer is not useful. Since hardcopy format is so application-dependent, it is difficult, if not impossible, to select a
reasonable subset of functionality that should be required on all compliant systems.</p>

<p>The term <i>unspecified</i> is used in this section in lieu of <i>implementation-defined</i> as most known implementations would
not be able to make definitive statements in their conformance documents; the existence and usage of printers is very dependent on
how the system administrator configures each individual system.</p>

<p>Since the default destination, device type, queuing mechanisms, and acceptable forms of input are all unspecified, usage
guidelines for what a conforming application can do are as follows:</p>

<ul>
<li>
<p>Use the command in a pipeline, or with <b>-c</b>, so that there are no permission problems and the files can be safely deleted
or modified.</p>
</li>

<li>
<p>Limit output to text files of reasonable line lengths and printable characters and include no device-specific formatting
information, such as a page description language. The meaning of &quot;reasonable&quot; in this context can only be answered as a
quality-of-implementation issue, but it should be apparent from historical usage patterns in the industry and the locale. The <a
href="../utilities/pr.html"><i>pr</i></a> and <a href="../utilities/fold.html"><i>fold</i></a> utilities can be used to achieve
reasonable formatting for the default page size of the implementation.</p>
</li>
</ul>

<p>Alternatively, the application can arrange its installation in such a way that it requires the system administrator or operator
to provide the appropriate information on <i>lp</i> options and environment variable values.</p>

<p>At a minimum, having this utility in this volume of IEEE&nbsp;Std&nbsp;1003.1-2001 tells the industry that conforming
applications require a means to print output and provides at least a command name and <i>LPDEST</i> routing mechanism that can be
used for discussions between vendors, application writers, and users. The use of &quot;should&quot; in the DESCRIPTION of <i>lp</i> clearly
shows the intent of the standard developers, even if they cannot mandate that all systems (such as laptops) have printers.</p>

<p>This volume of IEEE&nbsp;Std&nbsp;1003.1-2001 does not specify what the ownership of the process performing the writing to the
output device may be. If <b>-c</b> is not used, it is unspecified whether the process performing the writing to the output device
has permission to read <i>file</i> if there are any restrictions in place on who may read <i>file</i> until after it is printed.
Also, if <b>-c</b> is not used, the results of deleting <i>file</i> before it is printed are unspecified.</p>
</blockquote>

<h4><a name="tag_04_80_19"></a>FUTURE DIRECTIONS</h4>

<blockquote>
<p>None.</p>
</blockquote>

<h4><a name="tag_04_80_20"></a>SEE ALSO</h4>

<blockquote>
<p><a href="mailx.html"><i>mailx</i></a></p>
</blockquote>

<h4><a name="tag_04_80_21"></a>CHANGE HISTORY</h4>

<blockquote>
<p>First released in Issue 2.</p>
</blockquote>

<h4><a name="tag_04_80_22"></a>Issue 6</h4>

<blockquote>
<p>The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:</p>

<ul>
<li>
<p>In the DESCRIPTION, the requirement to associate a unique request ID, and the normal generation of a banner page is added.</p>
</li>

<li>
<p>In the OPTIONS section:</p>

<ul>
<li>
<p>The <b>-d</b> <i>dest</i> description is expanded, but references to <i>lpstat</i> are removed.</p>
</li>

<li>
<p>The <b>-m</b>, <b>-o</b>, <b>-s</b>, <b>-t</b>, and <b>-w</b> options are added.</p>
</li>
</ul>
</li>

<li>
<p>In the ENVIRONMENT VARIABLES section, <i>LC_TIME</i> may now affect the execution.</p>
</li>

<li>
<p>The STDOUT section is added.</p>
</li>
</ul>

<p>The normative text is reworded to avoid use of the term &quot;must&quot; for application requirements.</p>

<p>The <i>TZ</i> entry is added to the ENVIRONMENT VARIABLES section.</p>
</blockquote>

<div class="box"><em>End of informative text.</em></div>

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