---
layout: page
category-page: intermediate
category-title: Intermediate commands
tags: watch repeat track analyse seconds
author: Claudio Maggioni
title: watch
---
<p>
The <code>watch</code> command is a system utility able to execute a command
every <i>n</i> seconds by clearing the screen and displaying the
output of the command each time the interval is over. This command is very
simple to use and very effective: it can be used to check the size in bytes
of a file while downloading it, or it can be used on <i>Linux</i> to jiggle
around the mouse every ~5 minutes with the command <code>xdotool</code> in
order to keep the computer awake.

<h3>Usage</h3>

<code>watch</code> has a very simple syntax: the amount in seconds to wait
between executions is specified in seconds using the <code>-n</code> flag
and the default value is <i>2</i>. Also, differences between older and
newer outputs are highlighted if the <code>-d</code> flag is used.

Example: Watch the size of "ubuntu.iso" every 5 seconds

<pre>
watch -n 5 du -h ubuntu.iso
</pre>

Example: Watch the contents of "site.html" every 2 seconds and highlight the
differencies between iterations

<pre>
watch -d cat site.html
</pre>