---
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 <em>n</em> 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 <em>Linux</em> to jiggle
  around the mouse every ~5 minutes with the command <code>xdotool</code> in
  order to keep the computer awake.
</p>

<h3>Usage</h3>

<p>
  <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 <em>2</em>. Also, differences between older and 
  newer outputs are highlighted if the <code>-d</code> flag is used.
</p>

<h4>Watch the size of "ubuntu.iso" every 5 seconds</h4>

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

<h4>Watch the contents of "site.html" every 2 seconds and highlight the
  differencies between iterations</h4>

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