theshell.ch/site/pages/scripts/7-if.html

---
layout: page
category-page: scripts
category-title: Scripting
tags: if else script scripting read
author: Matteo Omenetti
title: If statement
previous-page: pages/scripts/6-while-loop.html
next-page: pages/scripts/8-redirection.html
---

<!-- Introduction -->
If statements allow us to make decisions in our Bash scripts. They allow us to
whether run or not a piece of code based on a condition that we set. <br>

If statements take this form:
{% highlight bash %}
if [condition]; then
    command1
    command2
    command3
    ...
fi
{% endhighlight %}

Anything between <code>then</code> and <code>fi</code> will be executed only if the condition
evaluates to true. <br>
Here is a simple example:

{% highlight bash %}
i=210;

if [$i -ge 200]; then
    echo "You chose a big number."
 fi
{% endhighlight %}

In this first example we evaluate a variable <code>i</code> to 105.
The <i> if statement </i> will print "You chose a big number"
only if the number contained in our variable <code>i</code> is <b>G</b>reater or
<b>E</b>qual to 200. <br>
This is our case, therefore the output of this piece of code will be:
<pre>
  You chose a big number.
</pre>
<!-- End of Introduction -->


<!-- If Else -->
<h3> If Else </h3>

Sometimes we want to perform a certain set of actions, if our condition evaluates to
true and another set of actions if our condition evaluates to false. We can do this with
the <i> if else </i> statement.
<i> if else </i> sattements take this form:
{% highlight bash %}
if [condition]; then
    command1
    command2
    command3
    ...
else
    command1
    command2
    command3
    ...
fi
{% endhighlight %}

Here is a simple example:
{% highlight bash %}
i=50;

if [$i -ge 200]; then
    echo "You chose a big number."
else
    echo "You chose a small number."
fi
{% endhighlight %}

In this example, that is just an extension of the previous example, we
evaluate a variable <code>i</code> to 50. If <code>i</code> is greater or equal to
200, you print out "You chose a big number", otherwise,
(if <code>i</code> is not greater or equal to 200), just like in this case, you print out
"You chose a small number".
Therefore, the output of this piece of code is:

<pre>
  You chose a small number.
</pre>
<!-- End of If Else -->


<!-- If Elif Else -->
<h3> If Elif Else </h3>
Sometimes, in programming, it is necessary to have a series of conditions that lead to
different paths. We can accommodate this need with the <i>if else elif</i> mechanism.
The <i>if else elif</i> mechanism takes this form:

{% highlight bash %}
if [condition]; then
    command1
    command2
    command3
    ...
elif [condition]; then
    command1
    command2
    command3
    ...
else
    command1
    command2
    command3
    ...
fi
{% endhighlight %}

Here is a simple example:

{% highlight bash %}
i=150;

if [$i -ge 200]; then
    echo "You chose a big number."
elif [$i == 150]; then
    echo "You chose 150".
else
    echo "You chose a small number"
fi
{% endhighlight %}

In this example, that is just an extension of the previous example, we evaluate a
variable <code>i</code> to 150. If <code>i</code> is greater or equal to 200,
you print out "You chose a big number", if <code>i</code> is equal to 150 you print out
"You chose 150" otherwise you print out "You chose a small number".
Therefore, the output of this piece of code is:

<pre>
  You chose 150.
</pre>