theshell.ch/site/pages/scripts/redirection.html

---
layout: page
category-page: scripts
category-title: Scripting
tags: redirect output input
author: Dario Rasic
title: Redirection
---
<p>

<h3>Output as input</h3>
<br>
To redirect a certain output of the command-line we have to use the symbol "&gt;".<br>

In this case, we will use a file named <i>hello.txt</i>, in which we want to insert
a certain output ("Sun" in this case):<br>

<pre>
echo "Sun" > hello.txt
</pre>

So if we print the content of the file in our command-line, the output will be the following:

<pre>
cat hello.txt
    Sun
</pre>

If we want to append a certain output to an existing file,
we just have to use "&gt;&gt;" symbols:

<pre>
cat hello.txt
    Sun
echo "Moon" >> hello.txt
cat hello.txt
    Sun
    Moon
</pre>

<!-- Input redirection text -->
<h3>Input as output</h3>
<br>
To redirect an input from a file for a command, the symbol "&lt;" is used.

<pre>
echo < $(cat hello.txt)
    Sun
    Moon
</pre>
<p>This is particularly useful when chaining commands.</p>
<br>
<!-- Chaining command text -->
<h3>Chaining (or Piping)</h3>
<br>
Chaining, also called Piping because it works with the pipe symbol "|", takes the output of a certain command-line and feeds it to another command in a direct way.
<!-- Table for the example of the piping command -->
<pre>
cat hello.txt | grep Mo
Moon
</pre>

<!-- A simple example -->
<h3>Simple Example</h3>
<br>
Now let's say that we want to combine those commands in a more complex operation. Let's say we want to take some contents from a certain file and put it into another file.<br>

We want to sort the animals whose name begins with letter "d"  from the file <i>animals.txt</i> and put it into <i>d_animals.txt</i>.<br>

<pre>
grep d < animals.txt > d_animals.txt
<br>
cat d_animals.txt
Deer
Dog
Dolphin
...
</pre>


</p>