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

---
layout: page
category-page: scripts
category-title: Scripting
tags: if else script scripting read
author: Matteo Omenetti
title: If Statement
---
<!-- Introduction -->
<p>
  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:
  <pre>
    if [condition]
      then
        command1
        command2
        command3
        ...
      fi
  </pre>

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

<pre>
  i=210;

  if [$i -ge 200]
    then
      echo You chose a big number.
  fi
</pre>

In this first example we evaluate a varibale <code>i</code> to 105. The <i> if statement </i> will print "You chose a big number"
only if the number contained in our varibale <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 condtion 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:
<pre>
  if [condition]
    then
      command1
      command2
      command3
      ...
    else
      command1
      command2
      command3
      ...
    fi
</pre>

Here is a simple example:
<pre>
  i=50;

  if [$i -ge 200]
    then
      echo You chose a big number.
    else
    echo You chose a small number.
  fi
</pre>
In this example, that is just an extention of the previuous example, we evealuate a variable <code>i</code>
to 50. If <code>i</code> is gretaer or equal to 200, you print out "You chose a big number", otherwise,
(if <code>i</code> is not gretaer 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 condtions that lead to different paths.
We can accomodate this need with the <i>if else elif</i> mechanism.
The <i>if else elif</i> mechanism takes this form:

<pre>
  if [condition]
    then
      command1
      command2
      command3
      ...
  elif [condition]
    then
      command1
      command2
      command3
      ...
  else
      command1
      command2
      command3
      ...
  fi
</pre>

Here is a simple example:

<pre>
  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
</pre>

  In this example, that is just an extention of the previuous example, we evealuate a variable <code>i</code>
  to 150. If <code>i</code> is gretaer 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>
<!-- End of If Elif Else -->















  </p>