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<li><a class="reference internal" href="#">commands – Run external shell commands</a><ul>
<li><a class="reference internal" href="#getstatusoutput">getstatusoutput()</a></li>
<li><a class="reference internal" href="#getoutput">getoutput()</a></li>
<li><a class="reference internal" href="#getstatus">getstatus()</a></li>
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<div class="section" id="module-commands">
<span id="commands-run-external-shell-commands"></span><h1>commands – Run external shell commands<a class="headerlink" href="#module-commands" title="Permalink to this headline">¶</a></h1>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">Purpose:</th><td class="field-body">The commands module contains utility functions for working with shell command output under Unix.</td>
</tr>
<tr class="field"><th class="field-name">Python Version:</th><td class="field-body">1.4</td>
</tr>
</tbody>
</table>
<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p class="last">This module is made obsolete by the <a class="reference internal" href="../subprocess/index.html#module-subprocess" title="subprocess: Work with additional processes"><tt class="xref py py-mod docutils literal"><span class="pre">subprocess</span></tt></a> module.</p>
</div>
<p>There are 3 functions in the commands module for working with external
commands. The functions are shell-aware and return the output or status code
from the command.</p>
<div class="section" id="getstatusoutput">
<h2>getstatusoutput()<a class="headerlink" href="#getstatusoutput" title="Permalink to this headline">¶</a></h2>
<p>The function getstatusoutput() runs a command via the shell and returns the
exit code and the text output (stdout and stderr combined). The exit codes are
the same as for the C function wait() or os.wait(). The code is a 16-bit
number. The low byte contains the signal number that killed the process. When
the signal is zero, the high byte is the exit status of the program. If a core
file was produced, the high bit of the low byte is set.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">commands</span> <span class="kn">import</span> <span class="o">*</span>
<span class="k">def</span> <span class="nf">run_command</span><span class="p">(</span><span class="n">cmd</span><span class="p">):</span>
<span class="k">print</span> <span class="s">'Running: "</span><span class="si">%s</span><span class="s">"'</span> <span class="o">%</span> <span class="n">cmd</span>
<span class="n">status</span><span class="p">,</span> <span class="n">text</span> <span class="o">=</span> <span class="n">getstatusoutput</span><span class="p">(</span><span class="n">cmd</span><span class="p">)</span>
<span class="n">exit_code</span> <span class="o">=</span> <span class="n">status</span> <span class="o">>></span> <span class="mi">8</span> <span class="c"># high byte</span>
<span class="n">signal_num</span> <span class="o">=</span> <span class="n">status</span> <span class="o">%</span> <span class="mi">256</span> <span class="c"># low byte</span>
<span class="k">print</span> <span class="s">'Status: x</span><span class="si">%04x</span><span class="s">'</span> <span class="o">%</span> <span class="n">status</span>
<span class="k">print</span> <span class="s">'Signal: x</span><span class="si">%02x</span><span class="s"> (</span><span class="si">%d</span><span class="s">)'</span> <span class="o">%</span> <span class="p">(</span><span class="n">signal_num</span><span class="p">,</span> <span class="n">signal_num</span><span class="p">)</span>
<span class="k">print</span> <span class="s">'Exit : x</span><span class="si">%02x</span><span class="s"> (</span><span class="si">%d</span><span class="s">)'</span> <span class="o">%</span> <span class="p">(</span><span class="n">exit_code</span><span class="p">,</span> <span class="n">exit_code</span><span class="p">)</span>
<span class="k">print</span> <span class="s">'Core? : </span><span class="si">%s</span><span class="s">'</span> <span class="o">%</span> <span class="nb">bool</span><span class="p">(</span><span class="n">signal_num</span> <span class="o">&</span> <span class="p">(</span><span class="mi">1</span> <span class="o"><<</span> <span class="mi">8</span><span class="p">))</span> <span class="c"># high bit</span>
<span class="k">print</span> <span class="s">'Output:'</span>
<span class="k">print</span> <span class="n">text</span>
<span class="k">print</span>
<span class="n">run_command</span><span class="p">(</span><span class="s">'ls -l *.py'</span><span class="p">)</span>
<span class="n">run_command</span><span class="p">(</span><span class="s">'ls -l *.notthere'</span><span class="p">)</span>
<span class="n">run_command</span><span class="p">(</span><span class="s">'./dumpscore'</span><span class="p">)</span>
<span class="n">run_command</span><span class="p">(</span><span class="s">'echo "WAITING TO BE KILLED"; read input'</span><span class="p">)</span>
</pre></div>
</div>
<p>This example runs two commands that exit normally, a third meant to generate a core dump, and a fourth that
blocks waiting to be killed from another shell. (Don’t simply use Ctrl-C as the interpreter will intercept that
signal. Use ps and grep in another window to find the read process and send it a signal with kill.)</p>
<div class="highlight-python"><pre>$ python commands_getstatusoutput.py
Running: "ls -l *.py"
Status: x0000
Signal: x00 (0)
Exit : x00 (0)
Core? : False
Output:
-rw-r--r-- 1 dhellmann dhellmann 1140 Mar 12 2009 __init__.py
-rw-r--r-- 1 dhellmann dhellmann 1297 Mar 12 2009 commands_getoutput.py
-rw-r--r--@ 1 dhellmann dhellmann 1355 Mar 12 2009 commands_getstatus.py
-rw-r--r--@ 1 dhellmann dhellmann 1739 Nov 26 12:52 commands_getstatusoutput.py
Running: "ls -l *.notthere"
Status: x0100
Signal: x00 (0)
Exit : x01 (1)
Core? : False
Output:
ls: *.notthere: No such file or directory
Running: "./dumpscore"
Status: x8600
Signal: x00 (0)
Exit : x86 (134)
Core? : False
Output:
sh: line 1: 47021 Abort trap (core dumped) ./dumpscore
Running: "echo "WAITING TO BE KILLED"; read input"
Status: x0001
Signal: x01 (1)
Exit : x00 (0)
Core? : False
Output:
WAITING TO BE KILLED</pre>
</div>
<p>In this example, I used <tt class="docutils literal"><span class="pre">kill</span> <span class="pre">-HUP</span> <span class="pre">$PID</span></tt> to kill the reading process from a separate shell window, so the
signal is reported as <tt class="docutils literal"><span class="pre">1</span></tt>.</p>
</div>
<div class="section" id="getoutput">
<h2>getoutput()<a class="headerlink" href="#getoutput" title="Permalink to this headline">¶</a></h2>
<p>If the exit code is not useful for your application, you can use getoutput()
to receive only the text output from the command.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">commands</span> <span class="kn">import</span> <span class="o">*</span>
<span class="n">text</span> <span class="o">=</span> <span class="n">getoutput</span><span class="p">(</span><span class="s">'ls -l *.py'</span><span class="p">)</span>
<span class="k">print</span> <span class="s">'ls -l *.py:'</span>
<span class="k">print</span> <span class="n">text</span>
<span class="k">print</span>
<span class="n">text</span> <span class="o">=</span> <span class="n">getoutput</span><span class="p">(</span><span class="s">'ls -l *.notthere'</span><span class="p">)</span>
<span class="k">print</span> <span class="s">'ls -l *.py:'</span>
<span class="k">print</span> <span class="n">text</span>
</pre></div>
</div>
<div class="highlight-python"><pre>$ python commands_getoutput.py
ls -l *.py:
-rw-r--r-- 1 dhellman dhellman 1191 Oct 21 09:41 __init__.py
-rw-r--r-- 1 dhellman dhellman 1321 Oct 21 09:48 commands_getoutput.py
-rw-r--r-- 1 dhellman dhellman 1265 Oct 21 09:50 commands_getstatus.py
-rw-r--r-- 1 dhellman dhellman 1626 Oct 21 10:10 commands_getstatusoutput.py
ls -l *.py:
ls: *.notthere: No such file or directory</pre>
</div>
</div>
<div class="section" id="getstatus">
<h2>getstatus()<a class="headerlink" href="#getstatus" title="Permalink to this headline">¶</a></h2>
<p>Contrary to what you might expect, getstatus() does not run a command and
return the status code. Instead, it’s argument is a filename which is combined
with “ls -ld” to build a command to be run by getoutput(). The text output of
the command is returned.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">commands</span> <span class="kn">import</span> <span class="o">*</span>
<span class="n">status</span> <span class="o">=</span> <span class="n">getstatus</span><span class="p">(</span><span class="s">'commands_getstatus.py'</span><span class="p">)</span>
<span class="k">print</span> <span class="s">'commands_getstatus.py:'</span><span class="p">,</span> <span class="n">status</span>
<span class="n">status</span> <span class="o">=</span> <span class="n">getstatus</span><span class="p">(</span><span class="s">'notthere.py'</span><span class="p">)</span>
<span class="k">print</span> <span class="s">'notthere.py:'</span><span class="p">,</span> <span class="n">status</span>
<span class="n">status</span> <span class="o">=</span> <span class="n">getstatus</span><span class="p">(</span><span class="s">'$filename'</span><span class="p">)</span>
<span class="k">print</span> <span class="s">'$filename:'</span><span class="p">,</span> <span class="n">status</span>
</pre></div>
</div>
<p>As you notice from the output, the $ character in the argument to the last
call is escaped so the environment variable name is not expanded.</p>
<div class="highlight-python"><pre>$ python commands_getstatus.py
commands_getstatus.py: -rw-r--r-- 1 dhellman dhellman 1387 Oct 21 10:19 commands_getstatus.py
notthere.py: ls: notthere.py: No such file or directory
$filename: ls: $filename: No such file or directory</pre>
</div>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt><a class="reference external" href="http://docs.python.org/library/commands.html">commands</a></dt>
<dd>The standard library documentation for this module.</dd>
<dt><a class="reference internal" href="../signal/index.html#module-signal" title="signal: Receive notification of asynchronous system events"><tt class="xref py py-mod docutils literal"><span class="pre">signal</span></tt></a></dt>
<dd>Defines constants for signals such as HUP (<tt class="docutils literal"><span class="pre">1</span></tt>).</dd>
</dl>
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