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<title>Execute an external program and display raw output</title>
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<h1 class="refname">passthru</h1>
<p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">passthru</span> — <span class="dc-title">Execute an external program and display raw output</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.passthru-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type"><span class="type void">void</span></span> <span class="methodname"><strong>passthru</strong></span>
( <span class="methodparam"><span class="type">string</span> <code class="parameter">$command</code></span>
[, <span class="methodparam"><span class="type">int</span> <code class="parameter reference">&$return_var</code></span>
] )</div>
<p class="para rdfs-comment">
The <span class="function"><strong>passthru()</strong></span> function is similar to the
<span class="function"><a href="function.exec.html" class="function">exec()</a></span> function in that it executes a
<em><code class="parameter">command</code></em>. This function
should be used in place of <span class="function"><a href="function.exec.html" class="function">exec()</a></span> or
<span class="function"><a href="function.system.html" class="function">system()</a></span> when the output from the Unix command
is binary data which needs to be passed directly back to the
browser. A common use for this is to execute something like the
pbmplus utilities that can output an image stream directly. By
setting the Content-type to <em>image/gif</em> and
then calling a pbmplus program to output a gif, you can create
PHP scripts that output images directly.
</p>
</div>
<div class="refsect1 parameters" id="refsect1-function.passthru-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<span class="term"><em><code class="parameter">command</code></em></span>
<dd>
<p class="para">
The command that will be executed.
</p>
</dd>
</dt>
<dt>
<span class="term"><em><code class="parameter">return_var</code></em></span>
<dd>
<p class="para">
If the <em><code class="parameter">return_var</code></em> argument is present, the
return status of the Unix command will be placed here.
</p>
</dd>
</dt>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.passthru-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
No value is returned.
</p>
</div>
<div class="refsect1 notes" id="refsect1-function.passthru-notes">
<h3 class="title">Notes</h3>
<div class="warning"><strong class="warning">Warning</strong><p class="para">When allowing user-supplied data to be
passed to this function, use
<span class="function"><a href="function.escapeshellarg.html" class="function">escapeshellarg()</a></span> or <span class="function"><a href="function.escapeshellcmd.html" class="function">escapeshellcmd()</a></span>
to ensure that users cannot trick the system into executing arbitrary
commands.</p></div>
<blockquote class="note"><p><strong class="note">Note</strong>: <p class="para">If a program is started with this function,
in order for it to continue running in the background, the output of the
program must be redirected to a file or another output stream. Failing to do so
will cause PHP to hang until the execution of the program ends.</p></p></blockquote>
<blockquote class="note"><p><strong class="note">Note</strong>: <span class="simpara">When
<a href="features.safe-mode.html" class="link">safe mode</a> is enabled, you can only
execute files within the <a href="ini.sect.safe-mode.html#ini.safe-mode-exec-dir" class="link">safe_mode_exec_dir</a>.
For practical reasons, it is currently not allowed to have <em>..</em>
components in the path to the executable.</span></p></blockquote>
<div class="warning"><strong class="warning">Warning</strong><p class="simpara">With <a href="features.safe-mode.html" class="link">safe mode</a> enabled,
the command string is escaped with <span class="function"><a href="function.escapeshellcmd.html" class="function">escapeshellcmd()</a></span>. Thus,
<em>echo y | echo x</em> becomes <em>echo y \| echo x</em>.</p></div>
</div>
<div class="refsect1 seealso" id="refsect1-function.passthru-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"> <span class="function"><a href="function.exec.html" class="function" rel="rdfs-seeAlso">exec()</a> - Execute an external program</span></li>
<li class="member"> <span class="function"><a href="function.system.html" class="function" rel="rdfs-seeAlso">system()</a> - Execute an external program and display the output</span></li>
<li class="member"> <span class="function"><a href="function.popen.html" class="function" rel="rdfs-seeAlso">popen()</a> - Opens process file pointer</span></li>
<li class="member"> <span class="function"><a href="function.escapeshellcmd.html" class="function" rel="rdfs-seeAlso">escapeshellcmd()</a> - Escape shell metacharacters</span></li>
<li class="member"><a href="language.operators.execution.html" class="link">backtick operator</a></li>
</ul>
</p>
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