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<body>
<div id="content">
<h1 class="title">AWK</h1>
<div id="table-of-contents">
<h2>Table of Contents</h2>
<div id="text-table-of-contents">
<ul>
<li><a href="#org1da1eff">1. AWK and GAWK</a>
<ul>
<li><a href="#orgb5fc0b9">1.1. Simple Description of AWK:</a>
<ul>
<li><a href="#orgf0d32ba">1.1.1. Typical uses of awk:</a></li>
</ul>
</li>
<li><a href="#org03371c5">1.2. Basic example</a></li>
<li><a href="#org87bb050">1.3. Better examples</a></li>
<li><a href="#orgaf95990">1.4. What else can be done</a></li>
<li><a href="#orga44b236">1.5. Resources</a></li>
</ul>
</li>
</ul>
</div>
</div>

<div id="outline-container-org1da1eff" class="outline-2">
<h2 id="org1da1eff"><span class="section-number-2">1</span> AWK and GAWK</h2>
<div class="outline-text-2" id="text-1">
<p>
<i>Dependencies:</i> In order to learn awk this can be necessary for you to learn before:
</p>
<ul class="org-ul">
<li>Unix Pipes</li>
<li>Shell Basics</li>
<li>Data Streams</li>
<li>Unix-like Operative Systems</li>
</ul>
<ul class="org-ul">
<li>Before we start learning grep please create the following file named <code>animals.txt</code></li>
</ul>
<pre class="example">
Animals Quantity
Dogs    32
Cats    17
Birds   25
Cows    7
Ducks   9
Pigs   12
</pre>
</div>

<div id="outline-container-orgb5fc0b9" class="outline-3">
<h3 id="orgb5fc0b9"><span class="section-number-3">1.1</span> Simple Description of AWK:</h3>
<div class="outline-text-3" id="text-1-1">
<p>
AWK is a programming language in UNIX, it is designed for text processing, but can be used for data extraction and reporting generation. As a programming language, the syntax of Awk would seem similar to the languages C, Python and Bash, among others.
</p>

<p>
(<b>Note</b> In this case GNU awk or GAWK will be covered, which is the <a href="https://www.gnu.org/philosophy/free-sw.html">GNU Project's</a> implementation of AWK. <b>End Note</b>)
</p>
</div>

<div id="outline-container-orgf0d32ba" class="outline-4">
<h4 id="orgf0d32ba"><span class="section-number-4">1.1.1</span> Typical uses of awk:</h4>
<div class="outline-text-4" id="text-1-1-1">
<ul class="org-ul">
<li>Text processing.</li>
<li>Data extraction.</li>
<li>Formatted text reports.</li>
<li>Arithmetic operations.</li>
<li>String operations.</li>
<li>Many more!.</li>
</ul>
</div>
</div>
</div>

<div id="outline-container-org03371c5" class="outline-3">
<h3 id="org03371c5"><span class="section-number-3">1.2</span> Basic example</h3>
<div class="outline-text-3" id="text-1-2">
<p>
The first program we will write is very simple, it will just print "hello world!":
</p>
<pre class="example">
$ echo "hello world!" | awk {'print'}
hello world
</pre>

<p>
<b>What just happened?</b>
<i>awk is a pattern matcher, in this case it got an input "hello world" and a pattern 'print', and awk applies pattern to each line of the input. That is why we see 'hello world' as a result.</i>
</p>

<p>
As we can see awk is a language that process an input file, in a nutshell this is what awk does:
</p>

<ol class="org-ol">
<li>Gets input, a pattern to look for, and a rule to apply.</li>
<li>Reads input.</li>
<li>Looks first line of input looking for pattern.</li>
<li>If a pattern is matched, then rule is applied.</li>
<li>Moves to next line until End of File.</li>
</ol>

<p>
Of course, awk can get multiple patterns and rules, but all of them are applied sequentially, we can also change awk behaviour so it looks at patterns and not at lines. 
</p>
</div>
</div>


<div id="outline-container-org87bb050" class="outline-3">
<h3 id="org87bb050"><span class="section-number-3">1.3</span> Better examples</h3>
<div class="outline-text-3" id="text-1-3">
<p>
With awk we can print the content of a file with:
</p>
<pre class="example">
$ awk '{print $0}' fruits.txt 
Animals Quantity
Dogs    32
Cats    17
Birds   25
Cows    7
Ducks   9
Pigs   12
</pre>

<p>
We can also print only the first field of text with $1
</p>
<pre class="example">
$ awk '{print $1}' fruits.txt 
Animals
Dogs
Cats
Birds
Cows
Ducks
Pigs
</pre>

<p>
We can also print only the second field of text with $2
</p>
<pre class="example">
$ awk '{print $2}' fruits.txt 
Quantity
32
17
25
7
9
12
</pre>


<p>
<b>What just happened?</b>
The "$0", "$1" and "$2" have a meaning similar to a shell script. Instead of the zero, first and second argument, they mean the entire current line, the first and second field of the input line, respectively.
</p>
</div>
</div>


<div id="outline-container-orgaf95990" class="outline-3">
<h3 id="orgaf95990"><span class="section-number-3">1.4</span> What else can be done</h3>
<div class="outline-text-3" id="text-1-4">
<p>
Cool stuff that you can do now with this new knowledge.
</p>
</div>
</div>

<div id="outline-container-orga44b236" class="outline-3">
<h3 id="orga44b236"><span class="section-number-3">1.5</span> Resources</h3>
<div class="outline-text-3" id="text-1-5">
<p>
<a href="https://www.gnu.org/software/gawk/manual/">Gawk: Effective AWK Programming</a>
<a href="https://learnbyexample.gitbooks.io/command-line-text-processing/content/gnu_awk.html">Learn by Example - AWK</a>
<a href="https://www.ibm.com/developerworks/library/l-awk1/">AWK by example - IBM</a>
<a href="http://www.grymoire.com/Unix/Awk.html">AWK - Grymoire</a>
<a href="https://www.tutorialspoint.com/awk/">AWK Tutorial - Tutorialspoint</a>
<a href="http://www.softpanorama.org/Tools/Awk/hello_world_in_awk.shtml">Hello World in AWK</a>
</p>
</div>
</div>
</div>
</div>
<div id="postamble" class="status">
<p class="date">Created: 2017-11-11 sáb 12:25</p>
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