57 lines
1.9 KiB
HTML
57 lines
1.9 KiB
HTML
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---
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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: loop for while range do
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author: Marco Tereh
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title: Loops
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---
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A very useful feature for scripting is loops; that is, the ability to write a repeating piece of code.<br>
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Loops take this form:
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<pre>
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[condition] do
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[repeated code]
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done
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</pre>
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In particular, there are two types of loops, for loops and while loops.<br>
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For loops are written like this:
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<pre>
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for [variable] in [list] do
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[code]
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done
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</pre>
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Their function is to <i>iterate</i> over a list. The list can take various forms, but the variable will always be
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one of its elements. In particular, it will be the first element of the list on the first iteration and advance by
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one element in every iteration after that. Most importantly, it can be accessed from inside the repeating code.<br>
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<br>
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The most basic kind of list is a numerical range, written like this:
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<pre>
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for i in {1..10}; do
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[code]
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done
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</pre>
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<code>{1..10}</code> means "the list of every number between 1 and 10 (inclusive)".
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<code>i</code> is the variable that will hold one of these numbers in every iteration.
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Here's a simple example of how to use it:
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<pre>
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for i in {1..10}; do
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echo $i;
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done
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</pre>
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<!-- TODO: insert the correct link here once the variables page is up -->
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<a href="#"><code>$i</code> is how you access the variable i</a>.
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Ranges can also count backward like this: <code>{10..1}</code>.
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Another way to say what <code>{1..10}</code> means is "The numbers between 10 and 1, <i>in increments of 1</i>".
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What if you want increments of two, though? What if you want every <i>even</i> number in a range?<br>
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Numerical ranges also allow you to specify the size of the increments or decrements between each element in the list,
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more generally called the <i>step size</i>.
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Here's an example:
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<pre>
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for i in {0..10..2}; do
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echo $i;
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done
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</pre>
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