a6515acdb9
git-svn-id: svn+ssh://atelier.inf.usi.ch/home/bevilj/group-1@254 a672b425-5310-4d7a-af5c-997e18724b81
142 lines
3.3 KiB
HTML
142 lines
3.3 KiB
HTML
---
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layout: page
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category-page: scripts
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category-title: Scripting
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tags: if else script scripting read
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author: Matteo Omenetti
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title: If statement
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previous-page: pages/scripts/6-while-loop.html
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next-page: pages/scripts/8-redirection.html
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---
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<!-- Introduction -->
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If statements allow us to make decisions in our Bash scripts. They allow us to
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whether run or not a piece of code based on a condition that we set. <br>
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If statements take this form:
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{% highlight bash %}
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if [condition]; then
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command1
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command2
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command3
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...
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fi
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{% endhighlight %}
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Anything between <code>then</code> and <code>fi</code> will be executed only if the condition
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evaluates to true. <br>
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Here is a simple example:
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{% highlight bash %}
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i=210;
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if [$i -ge 200]; then
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echo "You chose a big number."
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fi
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{% endhighlight %}
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In this first example we evaluate a variable <code>i</code> to 105.
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The <i> if statement </i> will print "You chose a big number"
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only if the number contained in our variable <code>i</code> is <b>G</b>reater or
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<b>E</b>qual to 200. <br>
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This is our case, therefore the output of this piece of code will be:
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<pre>
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You chose a big number.
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</pre>
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<!-- End of Introduction -->
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<!-- If Else -->
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<h3> If Else </h3>
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Sometimes we want to perform a certain set of actions, if our condition evaluates to
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true and another set of actions if our condition evaluates to false. We can do this with
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the <i> if else </i> statement.
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<i> if else </i> sattements take this form:
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{% highlight bash %}
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if [condition]; then
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command1
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command2
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command3
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...
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else
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command1
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command2
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command3
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...
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fi
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{% endhighlight %}
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Here is a simple example:
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{% highlight bash %}
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i=50;
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if [$i -ge 200]; then
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echo "You chose a big number."
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else
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echo "You chose a small number."
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fi
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{% endhighlight %}
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In this example, that is just an extension of the previous example, we
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evaluate a variable <code>i</code> to 50. If <code>i</code> is greater or equal to
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200, you print out "You chose a big number", otherwise,
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(if <code>i</code> is not greater or equal to 200), just like in this case, you print out
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"You chose a small number".
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Therefore, the output of this piece of code is:
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<pre>
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You chose a small number.
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</pre>
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<!-- End of If Else -->
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<!-- If Elif Else -->
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<h3> If Elif Else </h3>
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Sometimes, in programming, it is necessary to have a series of conditions that lead to
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different paths. We can accommodate this need with the <i>if else elif</i> mechanism.
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The <i>if else elif</i> mechanism takes this form:
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{% highlight bash %}
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if [condition]; then
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command1
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command2
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command3
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...
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elif [condition]; then
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command1
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command2
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command3
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...
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else
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command1
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command2
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command3
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...
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fi
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{% endhighlight %}
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Here is a simple example:
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{% highlight bash %}
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i=150;
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if [$i -ge 200]; then
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echo "You chose a big number."
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elif [$i == 150]; then
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echo "You chose 150".
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else
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echo "You chose a small number"
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fi
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{% endhighlight %}
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In this example, that is just an extension of the previous example, we evaluate a
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variable <code>i</code> to 150. If <code>i</code> is greater or equal to 200,
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you print out "You chose a big number", if <code>i</code> is equal to 150 you print out
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"You chose 150" otherwise you print out "You chose a small number".
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Therefore, the output of this piece of code is:
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<pre>
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You chose 150.
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</pre>
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