92 lines
2.3 KiB
HTML
92 lines
2.3 KiB
HTML
---
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layout: page
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author: Domenico Votta
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category-page: advanced
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category-title: Advanced commands
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tags: search for occurencies
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title: grep
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previous-page: pages/cmd/advanced/emacs.html
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next-page: pages/cmd/advanced/head-tail.html
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---
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<code>grep</code> is a command that allows you to search occurrences of one or more
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keywords in one or more files. Through some flags you can decide on the search criteria.
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The command grep is case sensitive (robot is different from Robot), but we will see how
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to ignore that.<br>
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Here we have two files named <code>example1.txt</code> and
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<code>example2.txt</code> that contain 5 elements, to test this command:
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<code>example1.txt</code>
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{% highlight bash %}
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Car
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Computer
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Robot
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Smartphone
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Videogame
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{% endhighlight %}
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<code>example2.txt</code>
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{% highlight bash %}
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Apple
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Computer
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Robot
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Microsoft
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Huawei
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{% endhighlight %}
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The syntax command is:
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<pre>grep [flag] [keyword] [file]</pre>
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You can put different flags together to refine the search.
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<pre>
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grep Robot example1.txt example2.txt (if you write robot you won't have the correspondence.)
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example1.txt: Robot
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example2.txt: Robot
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</pre>
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Your output will be this because grep found the keyword Robot in both files
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<h2>Flags</h2>
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Here a list that contains the main flags of these command:
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<ul>
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<li> <b>-i</b>: this flag ignores case sensitivity. Here we can write Robot or
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robot that grep will find the correspondence.
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<pre>
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grep -i robot example1.txt example2.txt
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example1.txt: Robot
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example2.txt: Robot
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</pre>
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</li>
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<li> <b>-v</b>: this flag ignores the keyword from the search.
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<pre>
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grep -i -v robot example1.txt example2.txt
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example1.txt:Car
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example1.txt:Computer
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example1.txt:Smartphone
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example1.txt:Videogame
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example2.txt:Apple
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example2.txt:Computer
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example2.txt:Microsoft
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example2.txt:Huawei
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</pre>
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</li>
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<li> <b>-c</b>: this flag indicates the number of times that the keyword appears in the file.
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<pre>
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grep -i -c robot example1.txt
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1
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</pre>
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(If in the file you would have had two times the keyword Robot, the output would have been 2)
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</li>
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<li> <b>-h</b>: Remove from the output the file name where it found the keyword
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<pre>
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grep -i -h apple example1.txt example2.txt
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Apple
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</pre>
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How you can see the output doesn't show the file name <code>example2.txt</code>
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</li>
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</ul>
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