---
layout: page
author: Domenico Votta
category-page: advanced
category-title: Advanced commands
tags: pipes redirect output input
title: Pipes
previous-page: pages/cmd/advanced/paste.html
next-page: pages/cmd/advanced/tr.html
---

The <code>pipes</code>, which in the shell are represented with the symbol | ,
are used to join two commands on the terminal, taking the output of the first
command and using it as input of the second.<br>
It is common to see the commands <code>grep</code> and <code>ps</code> together,
an example below.<br>

Example: lists all processes with your username
<pre>
ps aux | grep user
</pre>

Example: count the lines of a file, using the
<a href="{{ site.baseurl }}/pages/cmd/advanced/nl.html">nl</a> command
<pre>
cat example1.txt | nl
    1  Car
    2  Computer
    3  Robot
    4  Smartphone
    5  Videogame
</pre>

Example: passing expressions to <a href="{{ site.baseurl }}/pages/cmd/advanced/bc.html">bc</a>
to do calculations
<pre>
echo "(12 / 2 - 3) * 3 + 1.5" | bc
    10.5
</pre>

You can use the commands that you learned and put them together, always
respecting the logic of the command.