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<li class="toctree-l1"><a class="reference internal" href="tutorial_completers.html">Tutorial: Programmable Tab-Completion</a></li>
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<li class="toctree-l1"><a class="reference internal" href="tutorial_subproc_strings.html">Tutorial: Subprocess Strings</a></li>
<li class="toctree-l1"><a class="reference internal" href="tutorial_ptk.html">Tutorial: <code class="docutils literal notranslate"><span class="pre">prompt_toolkit</span></code> custom keybindings</a></li>
<li class="toctree-l1"><a class="reference internal" href="bash_to_xsh.html">Bash to Xonsh Translation Guide</a></li>
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<article role="main" id="furo-main-content">
<section id="tutorial">
<span id="id1"></span><h1>Tutorial<a class="headerlink" href="#tutorial" title="Link to this heading">¶</a></h1>
<p>xonsh is a shell language and command prompt. Unlike other shells, xonsh is
based on Python, with additional syntax added that makes calling subprocess
commands, manipulating the environment, and dealing with the file system
easy. The xonsh command prompt gives users interactive access to the xonsh
language.</p>
<p>While all Python code is also xonsh, not all Bash code can be used in xonsh.
That would defeat the purpose, and Python is better anyway! Still, xonsh is
Bash-wards compatible in the ways that matter, such as for running commands,
reading in the Bash environment, and utilizing Bash tab completion.</p>
<p>The purpose of this tutorial is to teach you xonsh. There are many excellent
guides out there for learning Python, and this will not join their ranks.
Similarly, you’d probably get the most out of this tutorial if you have already
used a command prompt or interactive interpreter.</p>
<p>Let’s dive in!</p>
<section id="starting-xonsh">
<h2>Starting xonsh<a class="headerlink" href="#starting-xonsh" title="Link to this heading">¶</a></h2>
<p>Assuming you have successfully installed xonsh (see <a class="reference external" href="http://xon.sh">http://xon.sh</a>),
you can start up the xonsh interpreter via the <code class="docutils literal notranslate"><span class="pre">xonsh</span></code> command. Suppose
you are in a lesser terminal:</p>
<div class="highlight-console notranslate"><div class="highlight"><pre><span></span><span class="gp">$ </span>xonsh
<span class="go">snail@home ~ @</span>
</pre></div>
</div>
<p>Now we are in a xonsh shell. Our username happens to be <code class="docutils literal notranslate"><span class="pre">snail</span></code>, our
hostname happens to be <code class="docutils literal notranslate"><span class="pre">home</span></code>, and we are in our home directory (<code class="docutils literal notranslate"><span class="pre">~</span></code>).
Alternatively, you can setup your terminal emulator (xterm, gnome-terminal,
etc) to run xonsh automatically when it starts up. This is recommended.</p>
</section>
<section id="basics">
<h2>Basics<a class="headerlink" href="#basics" title="Link to this heading">¶</a></h2>
<p>The xonsh language is based on Python, and the xonsh shell uses Python to
interpret any input it receives. This makes simple things, like arithmetic,
simple:</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="mi">1</span> <span class="o">+</span> <span class="mi">1</span>
<span class="go">2</span>
</pre></div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>From here on we’ll be using <code class="docutils literal notranslate"><span class="pre">>>></span></code> to prefix (or prompt) any
xonsh input. This follows the Python convention and helps trick
syntax highlighting, though <code class="docutils literal notranslate"><span class="pre">$</span></code> is more traditional for shells.</p>
</div>
<p>Since this is just Python, we are able to import modules, print values,
and use other built-in Python functionality:</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">sys</span>
<span class="gp">>>></span> <span class="nb">print</span><span class="p">(</span><span class="n">sys</span><span class="o">.</span><span class="n">version</span><span class="p">)</span>
<span class="go">3.4.2 |Continuum Analytics, Inc.| (default, Oct 21 2014, 17:16:37)</span>
<span class="go">[GCC 4.4.7 20120313 (Red Hat 4.4.7-1)]</span>
</pre></div>
</div>
<p>We can also create and use literal data types, such as ints, floats, lists,
sets, and dictionaries. Everything that you are used to if you already know
Python is there:</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">d</span> <span class="o">=</span> <span class="p">{</span><span class="s1">'xonsh'</span><span class="p">:</span> <span class="kc">True</span><span class="p">}</span>
<span class="gp">>>></span> <span class="n">d</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s1">'bash'</span><span class="p">,</span> <span class="kc">False</span><span class="p">)</span>
<span class="go">False</span>
</pre></div>
</div>
<p>The xonsh shell also supports multi-line input for more advanced flow control.
The multi-line mode is automatically entered whenever the first line of input
is not syntactically valid on its own. Multi-line mode is then exited when
enter (or return) is pressed when the cursor is in the first column.</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">if</span> <span class="kc">True</span><span class="p">:</span>
<span class="gp">...</span> <span class="nb">print</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="gp">...</span> <span class="k">else</span><span class="p">:</span>
<span class="gp">...</span> <span class="nb">print</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span>
<span class="gp">...</span>
<span class="go">1</span>
</pre></div>
</div>
<p>Flow control, of course, includes loops.</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">for</span> <span class="n">i</span><span class="p">,</span> <span class="n">x</span> <span class="ow">in</span> <span class="nb">enumerate</span><span class="p">(</span><span class="s1">'xonsh'</span><span class="p">):</span>
<span class="gp">...</span> <span class="nb">print</span><span class="p">(</span><span class="n">i</span><span class="p">,</span> <span class="n">x</span><span class="p">)</span>
<span class="gp">...</span>
<span class="go">0 x</span>
<span class="go">1 o</span>
<span class="go">2 n</span>
<span class="go">3 s</span>
<span class="go">4 h</span>
</pre></div>
</div>
<p>We can also define and call functions and classes. I’ll mostly spare you the
details, but this <em>is</em> pretty cool:</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">def</span> <span class="nf">f</span><span class="p">():</span>
<span class="gp">...</span> <span class="k">return</span> <span class="s2">"xonsh"</span>
<span class="gp">...</span>
<span class="gp">>>></span> <span class="n">f</span><span class="p">()</span>
<span class="go">'xonsh'</span>
</pre></div>
</div>
<p>For easier indentation, Shift+Tab will enter 4 spaces.
And that about wraps it up for the basics section. It is just like Python.</p>
</section>
<section id="environment-variables">
<h2>Environment Variables<a class="headerlink" href="#environment-variables" title="Link to this heading">¶</a></h2>
<p>Environment variables are written as <code class="docutils literal notranslate"><span class="pre">$</span></code> followed by a name. For example,
<code class="docutils literal notranslate"><span class="pre">$HOME</span></code>, <code class="docutils literal notranslate"><span class="pre">$PWD</span></code>, and <code class="docutils literal notranslate"><span class="pre">$PATH</span></code>.</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nv">$HOME</span>
<span class="go">'/home/snail'</span>
</pre></div>
</div>
<p>You can set (and export) environment variables like you would set any other
variable in Python. The same is true for deleting them too.</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nv">$GOAL</span> <span class="o">=</span> <span class="s1">'Become the Lord of the Files'</span>
<span class="gp">>>></span> <span class="nb">print</span><span class="p">(</span><span class="nv">$GOAL</span><span class="p">)</span>
<span class="go">Become the Lord of the Files</span>
<span class="gp">>>></span> <span class="k">del</span> <span class="nv">$GOAL</span>
<span class="gp">>>></span> <span class="nv">$NUM</span> <span class="o">=</span> <span class="s2">"123"</span>
<span class="gp">>>></span> <span class="nv">$EXT</span> <span class="o">=</span> <span class="nv">$NUM</span> <span class="o">+</span> <span class="s2">"456"</span>
<span class="gp">>>></span> <span class="nv">$EXT</span>
<span class="go">'123456'</span>
<span class="gp">>>></span> <span class="nv">$FNUM</span> <span class="o">=</span> <span class="sa">f</span><span class="s2">"</span><span class="si">{</span><span class="err">$</span><span class="n">NUM</span><span class="si">}</span><span class="s2">456"</span> <span class="c1"># Not working with Python 3.12+ (https://github.com/xonsh/xonsh/issues/5166).</span>
<span class="gp">>>></span> <span class="nv">$FNUM</span> <span class="o">=</span> <span class="s2">"</span><span class="si">{FILLME}</span><span class="s2">456"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">FILLME</span><span class="o">=</span><span class="nv">$NUM</span><span class="p">)</span>
<span class="gp">>>></span> <span class="nv">$FNUM</span>
<span class="go">'123456'</span>
<span class="gp">>>></span> <span class="s2">"</span><span class="si">%s</span><span class="s2">456"</span> <span class="o">%</span> <span class="nv">$NUM</span>
<span class="go">'123456'</span>
</pre></div>
</div>
<p>Very nice.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>To update <code class="docutils literal notranslate"><span class="pre">os.environ</span></code> when the xonsh environment changes set
<a class="reference internal" href="envvars.html#update-os-environ"><span class="std std-ref">$UPDATE_OS_ENVIRON</span></a> to <code class="docutils literal notranslate"><span class="pre">True</span></code>.</p>
</div>
<section id="the-environment-itself">
<h3>The Environment Itself <code class="docutils literal notranslate"><span class="pre">${...}</span></code><a class="headerlink" href="#the-environment-itself" title="Link to this heading">¶</a></h3>
<p>All environment variables live in the built-in <code class="docutils literal notranslate"><span class="pre">${...}</span></code> (aka <code class="docutils literal notranslate"><span class="pre">__xonsh__.env</span></code>) mapping.
You can access this mapping directly, but in most situations, you shouldn’t need to.</p>
<p>If you want for example to check if an environment variable is present in your current
session (say, in your awesome new <code class="docutils literal notranslate"><span class="pre">xonsh</span></code> script) you can use the membership operator:</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="s1">'HOME'</span> <span class="ow">in</span> <span class="k">$</span><span class="p">{</span><span class="o">...</span><span class="p">}</span>
<span class="go">True</span>
</pre></div>
</div>
<p>To get information about a specific environment variable you can use the
<a class="reference internal" href="api/_autosummary/cmd/xonsh.environ.html#xonsh.environ.Env.help" title="xonsh.environ.Env.help"><code class="xref py py-func docutils literal notranslate"><span class="pre">help()</span></code></a> method.</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">$</span><span class="p">{</span><span class="o">...</span><span class="p">}</span><span class="o">.</span><span class="n">help</span><span class="p">(</span><span class="s1">'XONSH_DEBUG'</span><span class="p">)</span>
</pre></div>
</div>
<p>One helpful method on the <code class="docutils literal notranslate"><span class="pre">${...}</span></code> is <a class="reference internal" href="api/_autosummary/cmd/xonsh.environ.html#xonsh.environ.Env.swap" title="xonsh.environ.Env.swap"><code class="xref py py-func docutils literal notranslate"><span class="pre">swap()</span></code></a>.
It can be used to temporarily set an environment variable:</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">with</span> <span class="k">$</span><span class="p">{</span><span class="o">...</span><span class="p">}</span><span class="o">.</span><span class="n">swap</span><span class="p">(</span><span class="n">SOMEVAR</span><span class="o">=</span><span class="s1">'foo'</span><span class="p">):</span>
<span class="gp">...</span> <span class="n">echo</span> <span class="nv">$SOMEVAR</span>
<span class="gp">...</span>
<span class="gp">...</span>
<span class="go">foo</span>
<span class="gp">>>></span> <span class="n">echo</span> <span class="nv">$SOMEVAR</span>
<span class="gp">>>></span>
</pre></div>
</div>
</section>
<section id="environment-lookup-with-expr">
<h3>Environment Lookup with <code class="docutils literal notranslate"><span class="pre">${<expr>}</span></code><a class="headerlink" href="#environment-lookup-with-expr" title="Link to this heading">¶</a></h3>
<p>The <code class="docutils literal notranslate"><span class="pre">$NAME</span></code> is great as long as you know the name of the environment
variable you want to look up. But what if you want to construct the name
programmatically, or read it from another variable? Enter the <code class="docutils literal notranslate"><span class="pre">${}</span></code>
operator.</p>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>In Bash, <code class="docutils literal notranslate"><span class="pre">$NAME</span></code> and <code class="docutils literal notranslate"><span class="pre">${NAME}</span></code> are syntactically equivalent.
In xonsh, they have separate meanings.</p>
</div>
<p>We can place any valid Python expression inside of the curly braces in
<code class="docutils literal notranslate"><span class="pre">${<expr>}</span></code>. This result of this expression will then be used to look up a
value in the environment. Here are a couple of examples in action:</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">x</span> <span class="o">=</span> <span class="s1">'USER'</span>
<span class="gp">>>></span> <span class="k">$</span><span class="p">{</span><span class="n">x</span><span class="p">}</span>
<span class="go">'snail'</span>
<span class="gp">>>></span> <span class="k">$</span><span class="p">{</span><span class="s1">'HO'</span> <span class="o">+</span> <span class="s1">'ME'</span><span class="p">}</span>
<span class="go">'/home/snail'</span>
</pre></div>
</div>
<p>Not bad, xonsh, not bad.</p>
</section>
<section id="environment-types">
<h3>Environment Types<a class="headerlink" href="#environment-types" title="Link to this heading">¶</a></h3>
<p>Like other variables in Python, environment variables have a type. Sometimes
this type is imposed based on the variable name. The current rules are pretty
simple:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">\w*PATH</span></code>: any variable whose name ends in PATH is a list of strings.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">\w*DIRS</span></code>: any variable whose name ends in DIRS is a list of strings.</p></li>
</ul>
<p>Futhermore, a number of predefined environment variables listed <a class="reference external" href="envvars.html">here</a> have a static type.
For example,
* <code class="docutils literal notranslate"><span class="pre">XONSH_HISTORY_SIZE</span></code>: is an int, and
* <code class="docutils literal notranslate"><span class="pre">CASE_SENSITIVE_COMPLETIONS</span></code>: is a boolean.</p>
<p>xonsh will automatically convert back and forth to untyped (string-only)
representations of the environment as needed (mostly by subprocess commands).
When in xonsh, you’ll always have the typed version.</p>
<p>Variables that do not match the rules above are converted to strings using <code class="docutils literal notranslate"><span class="pre">str</span></code>,
except they are <code class="docutils literal notranslate"><span class="pre">None</span></code>. In this case the empty string is used.</p>
<p>Here are a couple of
PATH examples:</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nv">$PATH</span>
<span class="go">['/home/snail/.local/bin', '/home/snail/sandbox/bin',</span>
<span class="go">'/home/snail/miniconda3/bin', '/usr/local/bin', '/usr/local/sbin',</span>
<span class="go">'/usr/bin', '/usr/sbin', '/bin', '/sbin', '.']</span>
<span class="gp">>>></span> <span class="nv">$LD_LIBRARY_PATH</span>
<span class="go">['/home/snail/.local/lib', '']</span>
</pre></div>
</div>
<p>Also note that <em>any</em> Python object can go into the environment. It is sometimes
useful to have more sophisticated types, like functions, in the environment.
There are handful of environment variables that xonsh considers special.
They can be seen on the <a class="reference external" href="envvars.html">Environment Variables page</a>.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>In subprocess mode, referencing an undefined environment variable
will produce an empty string. In Python mode, however, a
<code class="docutils literal notranslate"><span class="pre">KeyError</span></code> will be raised if the variable does not exist in the
environment.</p>
</div>
</section>
<section id="callable-environment-variables">
<h3>Callable Environment Variables<a class="headerlink" href="#callable-environment-variables" title="Link to this heading">¶</a></h3>
<p>In some cases you may want to have environment variable with dynamically created value.
Here is the example of callable environment variable:</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Stamp</span><span class="p">:</span>
<span class="gp">...</span> <span class="s2">"""Return current date as string representation."""</span>
<span class="gp">...</span> <span class="k">def</span> <span class="fm">__repr__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">...</span> <span class="kn">from</span> <span class="nn">datetime</span> <span class="kn">import</span> <span class="n">datetime</span>
<span class="gp">...</span> <span class="k">return</span> <span class="nb">str</span><span class="p">(</span><span class="n">datetime</span><span class="o">.</span><span class="n">now</span><span class="p">()</span><span class="o">.</span><span class="n">isoformat</span><span class="p">())</span>
<span class="gp">...</span>
<span class="gp">...</span>
<span class="gp">>>></span> <span class="nv">$DT</span> <span class="o">=</span> <span class="n">Stamp</span><span class="p">()</span>
<span class="gp">>>></span> <span class="nv">$DT</span>
<span class="go">2024-11-11T11:11:22</span>
<span class="gp">>>></span> <span class="n">echo</span> <span class="nv">$DT</span>
<span class="go">2024-11-11T11:11:33</span>
<span class="gp">>>></span> <span class="n">env</span> <span class="o">|</span> <span class="n">grep</span> <span class="n">DT</span>
<span class="go">DT=2024-11-11T11:11:44</span>
</pre></div>
</div>
</section>
</section>
<section id="running-commands">
<h2>Running Commands<a class="headerlink" href="#running-commands" title="Link to this heading">¶</a></h2>
<p>As a shell, xonsh is meant to make running commands easy and fun.
Running subprocess commands should work like in any other shell.</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">echo</span> <span class="s2">"Yoo hoo"</span>
<span class="go">Yoo hoo</span>
<span class="gp">>>></span> <span class="n">cd</span> <span class="n">xonsh</span>
<span class="gp">>>></span> <span class="n">ls</span>
<span class="go">build docs README.rst setup.py xonsh __pycache__</span>
<span class="go">dist license scripts tests xonsh.egg-info</span>
<span class="gp">>>></span> <span class="nb">dir</span> <span class="n">scripts</span>
<span class="go">xonsh xonsh.bat</span>
<span class="gp">>>></span> <span class="n">git</span> <span class="n">status</span>
<span class="go">On branch main</span>
<span class="go">Your branch is up-to-date with 'origin/main'.</span>
<span class="go">Changes not staged for commit:</span>
<span class="go"> (use "git add <file>..." to update what will be committed)</span>
<span class="go"> (use "git checkout -- <file>..." to discard changes in working directory)</span>
<span class="go"> modified: docs/tutorial.rst</span>
<span class="go">no changes added to commit (use "git add" and/or "git commit -a")</span>
<span class="gp">>>></span> <span class="n">exit</span>
</pre></div>
</div>
<p>This should feel very natural.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Access the last run subprocess command using <code class="docutils literal notranslate"><span class="pre">__xonsh__.last</span></code>;
e.g. to get the return code, run <code class="docutils literal notranslate"><span class="pre">__xonsh__.last.rtn</span></code>.</p>
</div>
</section>
<section id="python-mode-vs-subprocess-mode">
<h2>Python-mode vs Subprocess-mode<a class="headerlink" href="#python-mode-vs-subprocess-mode" title="Link to this heading">¶</a></h2>
<p>It is sometimes helpful to make the distinction between lines that operate
in pure Python mode and lines that use shell-specific syntax, edit the
execution environment, and run commands. Unfortunately, it is not always
clear from the syntax alone what mode is desired. This ambiguity stems from
most command line utilities looking a lot like Python operators.</p>
<p>Take the case of <code class="docutils literal notranslate"><span class="pre">ls</span> <span class="pre">-l</span></code>. This is valid Python code, though it could
have also been written as <code class="docutils literal notranslate"><span class="pre">ls</span> <span class="pre">-</span> <span class="pre">l</span></code> or <code class="docutils literal notranslate"><span class="pre">ls-l</span></code>. So how does xonsh know
that <code class="docutils literal notranslate"><span class="pre">ls</span> <span class="pre">-l</span></code> is meant to be run in subprocess-mode?</p>
<p>For any given line that only contains an expression statement (expr-stmt,
see the Python AST docs for more information), if all the names cannot
be found as current variables xonsh will try to parse the line as a
subprocess command instead. In the above, if <code class="docutils literal notranslate"><span class="pre">ls</span></code> and <code class="docutils literal notranslate"><span class="pre">l</span></code> are not
variables, then subprocess mode will be attempted. If parsing in subprocess
mode fails, then the line is left in Python-mode.</p>
<p>In the following example, we will list the contents of the directory
with <code class="docutils literal notranslate"><span class="pre">ls</span> <span class="pre">-l</span></code>. Then we’ll make new variable names <code class="docutils literal notranslate"><span class="pre">ls</span></code> and <code class="docutils literal notranslate"><span class="pre">l</span></code> and then
subtract them. Finally, we will delete <code class="docutils literal notranslate"><span class="pre">ls</span></code> and <code class="docutils literal notranslate"><span class="pre">l</span></code> and be able to list
the directories again.</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="c1"># this will be in subproc-mode, because ls doesn't exist</span>
<span class="gp">>>></span> <span class="n">ls</span> <span class="o">-</span><span class="n">l</span>
<span class="go">total 0</span>
<span class="go">-rw-rw-r-- 1 snail snail 0 Mar 8 15:46 xonsh</span>
<span class="gp">>>></span> <span class="c1"># set ls and l variables to force python-mode</span>
<span class="gp">>>></span> <span class="n">ls</span> <span class="o">=</span> <span class="mi">44</span>
<span class="gp">>>></span> <span class="n">l</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">>>></span> <span class="n">ls</span> <span class="o">-</span><span class="n">l</span>
<span class="go">42</span>
<span class="gp">>>></span> <span class="c1"># deleting ls will return us to subproc-mode</span>
<span class="gp">>>></span> <span class="k">del</span> <span class="n">ls</span>
<span class="gp">>>></span> <span class="n">ls</span> <span class="o">-</span><span class="n">l</span>
<span class="go">total 0</span>
<span class="go">-rw-rw-r-- 1 snail snail 0 Mar 8 15:46 xonsh</span>
</pre></div>
</div>
<p>The determination between Python- and subprocess-modes is always done in the
safest possible way. If anything goes wrong, it will favor Python-mode.
The determination between the two modes is done well ahead of any execution.
You do not need to worry about partially executed commands - that is
impossible.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>If you would like to explicitly run a subprocess command, you can always
use the formal xonsh subprocess syntax that we will see in the following
sections. For example: <code class="docutils literal notranslate"><span class="pre">![ls</span> <span class="pre">-l]</span></code>.</p>
</div>
</section>
<section id="quoting">
<h2>Quoting<a class="headerlink" href="#quoting" title="Link to this heading">¶</a></h2>
<p>Single or double quotes can be used to remove the special meaning
of certain characters or words to xonsh. If a subprocess command
contains characters that collide with xonsh syntax then quotes
must be used to force xonsh to not interpret them.</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">echo</span> <span class="k">$</span><span class="p">{</span>
<span class="gp">...</span>
<span class="go">SyntaxError: <xonsh-code>:1:5: ('code: {',)</span>
<span class="go">echo ${</span>
<span class="go"> ^</span>
<span class="gp">>>></span> <span class="n">echo</span> <span class="s1">'${'</span>
<span class="go">${</span>
</pre></div>
</div>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>There is no notion of an escaping character in xonsh like the
backslash (\) in bash.</p>
</div>
</section>
<section id="captured-subprocess-with-and">
<h2>Captured Subprocess with <code class="docutils literal notranslate"><span class="pre">$()</span></code> and <code class="docutils literal notranslate"><span class="pre">!()</span></code><a class="headerlink" href="#captured-subprocess-with-and" title="Link to this heading">¶</a></h2>
<p>The <code class="docutils literal notranslate"><span class="pre">$(<expr>)</span></code> operator in xonsh executes a subprocess command and
<em>captures</em> some information about that command.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">$()</span></code> syntax captures and returns the standard output stream of the
command as a Python string. This is similar to how <code class="docutils literal notranslate"><span class="pre">$()</span></code> performs in Bash.
For example,</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">$</span><span class="p">(</span><span class="nb">ls</span> -l<span class="p">)</span>
<span class="go">'total 0\n-rw-rw-r-- 1 snail snail 0 Mar 8 15:46 xonsh\n'</span>
</pre></div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>By default the output is represented as one single block of output with new
line characters. You can set <code class="docutils literal notranslate"><span class="pre">$XONSH_SUBPROC_OUTPUT_FORMAT</span></code> to <code class="docutils literal notranslate"><span class="pre">list_lines</span></code>
to have a list of distinct lines in the commands like <code class="docutils literal notranslate"><span class="pre">du</span> <span class="pre">-h</span> <span class="pre">$(ls)</span></code>.</p>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre">!()</span></code> syntax captured more information about the command, as an instance
of a class called <code class="docutils literal notranslate"><span class="pre">CommandPipeline</span></code>. This object contains more information
about the result of the given command, including the return code, the process
id, the standard output and standard error streams, and information about how
input and output were redirected. For example:</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">!</span><span class="p">(</span><span class="nb">ls</span> nonexistent_directory<span class="p">)</span>
<span class="go">CommandPipeline(</span>
<span class="go"> pid=26968,</span>
<span class="go"> returncode=2,</span>
<span class="go"> args=['ls', 'nonexistent_directory'],</span>
<span class="go"> alias=['ls', '--color=auto', '-v'],</span>
<span class="go"> timestamps=[1485235484.5016758, None],</span>
<span class="go"> executed_cmd=['ls', '--color=auto', '-v', 'nonexistent_directory'],</span>
<span class="go"> input=None,</span>
<span class="go"> output=,</span>
<span class="go"> errors=None</span>
<span class="go">)</span>
</pre></div>
</div>
<p>The captured object <code class="docutils literal notranslate"><span class="pre">!()</span></code> operator allows for non-blocking execution.
You can call a long-running command, intersperse other commands and
read the captured output later:</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">p</span> <span class="o">=</span> <span class="k">!</span><span class="p">(</span><span class="nb">echo</span> snail<span class="p">)</span>
<span class="gp">>>></span> <span class="n">p</span><span class="o">.</span><span class="n">output</span>
<span class="go">''</span>
<span class="gp">>>></span> <span class="n">p</span><span class="o">.</span><span class="n">end</span><span class="p">()</span>
<span class="gp">>>></span> <span class="n">p</span><span class="o">.</span><span class="n">output</span>
<span class="go">'snail'</span>
</pre></div>
</div>
<p>You can force <code class="docutils literal notranslate"><span class="pre">xonsh</span></code> to block and wait for the command to complete by asking for the return code,
printing the object or reading the <code class="docutils literal notranslate"><span class="pre">out</span></code> attribute:</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">p</span> <span class="o">=</span> <span class="k">!</span><span class="p">(</span><span class="nb">echo</span> snail<span class="p">)</span>
<span class="gp">>>></span> <span class="n">p</span><span class="o">.</span><span class="n">out</span>
<span class="go">'snail'</span>
<span class="gp">>>></span> <span class="n">p</span> <span class="o">=</span> <span class="k">!</span><span class="p">(</span><span class="nb">echo</span> party<span class="p">)</span>
<span class="gp">>>></span> <span class="n">p</span><span class="o">.</span><span class="n">rtn</span>
<span class="go">0</span>
<span class="gp">>>></span> <span class="n">p</span><span class="o">.</span><span class="n">output</span>
<span class="go">'party'</span>
</pre></div>
</div>
<p>This object will be “truthy” if its return code was 0, and it is equal (via
<code class="docutils literal notranslate"><span class="pre">==</span></code>) to its return code. It also hashes to its return code. Converting the object
to the string will return the output. This allows for some interesting new
kinds of interactions with subprocess commands, for example:</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">check_file</span><span class="p">(</span><span class="n">file</span><span class="p">):</span>
<span class="go"> if !(test -e @(file)):</span>
<span class="go"> if !(test -f @(file)) or !(test -d @(file)):</span>
<span class="go"> print("File is a regular file or directory")</span>
<span class="go"> else:</span>
<span class="go"> print("File is not a regular file or directory")</span>
<span class="go"> else:</span>
<span class="go"> print("File does not exist")</span>
<span class="go">def wait_until_google_responds():</span>
<span class="go"> while not !(ping -c 1 google.com):</span>
<span class="go"> sleep 1</span>
</pre></div>
</div>
<p>If you iterate over the <code class="docutils literal notranslate"><span class="pre">CommandPipeline</span></code> object, it will yield lines of its
output. Using this, you can quickly and cleanly process output from commands.
Additionally, these objects expose a method <code class="docutils literal notranslate"><span class="pre">itercheck</span></code>, which behaves the same
as the built-in iterator but raises <code class="docutils literal notranslate"><span class="pre">XonshCalledProcessError</span></code> if the process
had a nonzero return code.</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">get_wireless_interface</span><span class="p">():</span>
<span class="go"> """Returns devicename of first connected wifi, None otherwise"""</span>
<span class="go"> for line in !(nmcli device):</span>
<span class="go"> dev, typ, state, conn_name = line.split(None, 3)</span>
<span class="go"> if typ == 'wifi' and state == 'connected':</span>
<span class="go"> return dev</span>
<span class="go">def grep_path(path, regexp):</span>
<span class="go"> """Recursively greps `path` for perl `regexp`</span>
<span class="go"> Returns a dict of 'matches' and 'failures'.</span>
<span class="go"> Matches are files that contain the given regexp.</span>
<span class="go"> Failures are files that couldn't be scanned.</span>
<span class="go"> """</span>
<span class="go"> matches = []</span>
<span class="go"> failures = []</span>
<span class="go"> try:</span>
<span class="go"> for match in !(grep -RPl @(regexp) @(str(path))).itercheck():</span>
<span class="go"> matches.append(match)</span>
<span class="go"> except XonshCalledProcessError as error:</span>
<span class="go"> for line in error.stderr.split('\n'):</span>
<span class="go"> if not line.strip():</span>
<span class="go"> continue</span>
<span class="go"> filename = line.split('grep: ', 1)[1].rsplit(':', 1)[0]</span>
<span class="go"> failures.append(filename)</span>
<span class="go"> return {'matches': matches, 'failures': failures}</span>
</pre></div>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre">$()</span></code> and <code class="docutils literal notranslate"><span class="pre">!()</span></code> operators are expressions themselves. This means that
we can assign the results to a variable or perform any other manipulations we
want.</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">x</span> <span class="o">=</span> <span class="k">$</span><span class="p">(</span><span class="nb">ls</span> -l<span class="p">)</span>
<span class="gp">>>></span> <span class="nb">print</span><span class="p">(</span><span class="n">x</span><span class="o">.</span><span class="n">upper</span><span class="p">())</span>
<span class="go">TOTAL 0</span>
<span class="go">-RW-RW-R-- 1 SNAIL SNAIL 0 MAR 8 15:46 XONSH</span>
<span class="gp">>>></span> <span class="n">y</span> <span class="o">=</span> <span class="k">!</span><span class="p">(</span><span class="nb">ls</span> -l<span class="p">)</span>
<span class="gp">>>></span> <span class="nb">print</span><span class="p">(</span><span class="n">y</span><span class="o">.</span><span class="n">returncode</span><span class="p">)</span>
<span class="go">0</span>
<span class="gp">>>></span> <span class="nb">print</span><span class="p">(</span><span class="n">y</span><span class="o">.</span><span class="n">rtn</span><span class="p">)</span> <span class="c1"># alias to returncode</span>
<span class="go">0</span>
</pre></div>
</div>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>Job control is not implemented for captured subprocesses.</p>
</div>
<p>While in subprocess-mode or inside of a captured subprocess, we can always
still query the environment with <code class="docutils literal notranslate"><span class="pre">$NAME</span></code> variables or the <code class="docutils literal notranslate"><span class="pre">${}</span></code> syntax,
or inject Python values with the <code class="docutils literal notranslate"><span class="pre">@()</span></code> operator:</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">$</span><span class="p">(</span><span class="nb">echo</span> <span class="nv">$HOME</span><span class="p">)</span>
<span class="go">'/home/snail'</span>
</pre></div>
</div>
</section>
<section id="threading">
<h2>Threading<a class="headerlink" href="#threading" title="Link to this heading">¶</a></h2>
<p>If you want to work more closely with captured commands, you need to know about threading.
Xonsh has a threading prediction mechanism that allows it to understand which commands can capture everything.
For example, the <code class="docutils literal notranslate"><span class="pre">echo</span></code> command has no interaction with the user and is capturable.
However, some tools have mixed behavior and can be run for either interactive or non-interactive tasks.
The best example of this is <code class="docutils literal notranslate"><span class="pre">ssh</span></code>, which allows for remote terminal sessions and executing commands.</p>
<p>To handle different types of tasks, xonsh has the <code class="docutils literal notranslate"><span class="pre">@thread</span></code> and <code class="docutils literal notranslate"><span class="pre">@unthread</span></code> built-in decorator aliases.
If you need to capture the output from an interactive tool that has a capturable mode use <code class="docutils literal notranslate"><span class="pre">@thread</span></code> to run:</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="o">@</span> <span class="k">!</span><span class="p">(</span><span class="nb">@thread</span> ssh host -T <span class="s1">'echo remote'</span><span class="p">)</span>
<span class="go">CommandPipeline(output="remote")</span>
</pre></div>
</div>
</section>
<section id="uncaptured-subprocess-with-and">
<h2>Uncaptured Subprocess with <code class="docutils literal notranslate"><span class="pre">$[]</span></code> and <code class="docutils literal notranslate"><span class="pre">![]</span></code><a class="headerlink" href="#uncaptured-subprocess-with-and" title="Link to this heading">¶</a></h2>
<p>Uncaptured subprocesses are denoted with the <code class="docutils literal notranslate"><span class="pre">$[]</span></code> and <code class="docutils literal notranslate"><span class="pre">![]</span></code> operators. They are
the same as <code class="docutils literal notranslate"><span class="pre">$()</span></code> captured subprocesses in almost every way. The only
difference is that the subprocess’s stdout passes directly through xonsh and
to the screen. The return value of <code class="docutils literal notranslate"><span class="pre">$[]</span></code> is always <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
<p>In the following, we can see that the results of <code class="docutils literal notranslate"><span class="pre">$[]</span></code> are automatically
printed, and that the return value is not a string.</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">x</span> <span class="o">=</span> <span class="k">$</span><span class="p">[</span><span class="nb">ls</span> -l<span class="p">]</span>
<span class="go">total 0</span>
<span class="go">-rw-rw-r-- 1 snail snail 0 Mar 8 15:46 xonsh</span>
<span class="gp">>>></span> <span class="n">x</span> <span class="ow">is</span> <span class="kc">None</span>
<span class="go">True</span>
</pre></div>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre">![]</span></code> operator is similar to the <code class="docutils literal notranslate"><span class="pre">!()</span></code> in that it returns an object
containing information about the result of executing the given command.
However, its standard output and standard error streams are directed to the
terminal, and the resulting object is not displayed. For example</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">x</span> <span class="o">=</span> <span class="k">!</span><span class="p">[</span><span class="nb">ls</span> -l<span class="p">]</span> <span class="ow">and</span> <span class="k">!</span><span class="p">[</span><span class="nb">echo</span> <span class="s2">"hi"</span><span class="p">]</span>
<span class="go">total 0</span>
<span class="go">-rw-rw-r-- 1 snail snail 0 Mar 8 15:46 xonsh</span>
<span class="go">hi</span>
</pre></div>
</div>
</section>
<section id="python-evaluation-with">
<h2>Python Evaluation with <code class="docutils literal notranslate"><span class="pre">@()</span></code><a class="headerlink" href="#python-evaluation-with" title="Link to this heading">¶</a></h2>
<p>The <code class="docutils literal notranslate"><span class="pre">@(<expr>)</span></code> operator form works in subprocess mode, and will evaluate
arbitrary Python code. The result is appended to the subprocess command list.
If the result is a string or bytes, it is appended to the argument list. If the result
is a list or other non-string sequence, the contents are converted to strings
and appended to the argument list in order. If the result in the first position
is a function, it is treated as an alias (see the section on <a class="reference internal" href="#aliases">Aliases</a> below),
even if it was not explicitly added to the <code class="docutils literal notranslate"><span class="pre">aliases</span></code> mapping. Otherwise, the
result is automatically converted to a string. For example,</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">x</span> <span class="o">=</span> <span class="s1">'xonsh'</span>
<span class="gp">>>></span> <span class="n">y</span> <span class="o">=</span> <span class="s1">'party'</span>
<span class="gp">>>></span> <span class="n">echo</span> <span class="k">@</span><span class="p">(</span><span class="n">x</span> <span class="o">+</span> <span class="s1">' '</span> <span class="o">+</span> <span class="n">y</span><span class="p">)</span>
<span class="go">xonsh party</span>
<span class="gp">>>></span> <span class="n">echo</span> <span class="k">@</span><span class="p">(</span><span class="mi">2</span><span class="o">+</span><span class="mi">2</span><span class="p">)</span>
<span class="go">4</span>
<span class="gp">>>></span> <span class="n">echo</span> <span class="k">@</span><span class="p">([</span><span class="mi">42</span><span class="p">,</span> <span class="s1">'yo'</span><span class="p">])</span>
<span class="go">42 yo</span>
<span class="gp">>>></span> <span class="n">echo</span> <span class="s2">"hello"</span> <span class="o">|</span> <span class="k">@</span><span class="p">(</span><span class="k">lambda</span> <span class="n">a</span><span class="p">,</span> <span class="n">s</span><span class="o">=</span><span class="kc">None</span><span class="p">:</span> <span class="n">s</span><span class="o">.</span><span class="n">read</span><span class="p">()</span><span class="o">.</span><span class="n">strip</span><span class="p">()</span> <span class="o">+</span> <span class="s2">" world</span><span class="se">\n</span><span class="s2">"</span><span class="p">)</span>
<span class="go">hello world</span>
<span class="gp">>>></span> <span class="k">@</span><span class="p">([</span><span class="s1">'echo'</span><span class="p">,</span> <span class="s1">'hello'</span><span class="p">,</span> <span class="s1">'world'</span><span class="p">])</span>
<span class="go">hello world</span>
<span class="gp">>>></span> <span class="k">@</span><span class="p">(</span><span class="s1">'echo hello world'</span><span class="p">)</span> <span class="c1"># note that strings are not split automatically</span>
<span class="go">xonsh: subprocess mode: command not found: echo hello world</span>
</pre></div>
</div>
<p>This syntax can be used inside of a captured or uncaptured subprocess, and can
be used to generate any of the tokens in the subprocess command list.</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">out</span> <span class="o">=</span> <span class="k">$</span><span class="p">(</span><span class="nb">echo</span> <span class="k">@</span><span class="p">(</span><span class="n">x</span> <span class="o">+</span> <span class="s1">' '</span> <span class="o">+</span> <span class="n">y</span><span class="p">))</span>
<span class="gp">>>></span> <span class="n">out</span>
<span class="go">'xonsh party'</span>
<span class="gp">>>></span> <span class="k">@</span><span class="p">(</span><span class="s2">"ech"</span> <span class="o">+</span> <span class="s2">"o"</span><span class="p">)</span> <span class="s2">"hey"</span>
<span class="go">hey</span>
</pre></div>
</div>
<p>Thus, <code class="docutils literal notranslate"><span class="pre">@()</span></code> allows us to create complex commands in Python-mode and then
feed them to a subprocess as needed. For example:</p>
<div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">20</span><span class="p">):</span>
<span class="go"> $[touch @('file%02d' % i)]</span>
</pre></div>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre">@()</span></code> syntax may also be used inside of subprocess
arguments, not just as a stand-alone argument. For example:</p>
<blockquote>
<div><div class="highlight-xonshcon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">x</span> <span class="o">=</span> <span class="s1">'hello'</span>
<span class="gp">>>></span> <span class="n">echo</span> <span class="o">/</span><span class="n">path</span><span class="o">/</span><span class="n">to</span><span class="o">/</span><span class="k">@</span><span class="p">(</span><span class="n">x</span><span class="p">)</span>
<span class="go">/path/to/hello</span>
</pre></div>
</div>
</div></blockquote>
<p>When used inside of a subprocess argument and <code class="docutils literal notranslate"><span class="pre"><expr></span></code> evaluates to a
non-string iterable, <code class="docutils literal notranslate"><span class="pre">@()</span></code> will expand to the outer product of all
given values:</p>
<blockquote>
<div><div class="highlight-sh notranslate"><div class="highlight"><pre><span></span>>>><span class="w"> </span><span class="nb">echo</span><span class="w"> </span>/path/to/@<span class="o">([</span><span class="s1">'hello'</span>,<span class="w"> </span><span class="s1">'world'</span><span class="o">])</span>
/path/to/hello<span class="w"> </span>/path/to/world
>>><span class="w"> </span><span class="nb">echo</span><span class="w"> </span>@<span class="o">([</span><span class="s1">'a'</span>,<span class="w"> </span><span class="s1">'b'</span><span class="o">])</span>:@<span class="o">(</span><span class="s1">'x'</span>,<span class="w"> </span><span class="s1">'y'</span><span class="o">)</span>