79 lines
1.7 KiB
HTML
79 lines
1.7 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: redirect output input
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author: Dario Rasic
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title: Redirection
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previous-page: pages/scripts/7-if.html
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---
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<h3>output as input</h3>
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<br>
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To redirect a certain output of the command-line we have to use the symbol ">".<br>
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In this case, we will use a file named <i>hello.txt</i>, in which we want to insert
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a certain output ("Sun" in this case):<br>
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<pre>
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echo "Sun" > hello.txt
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</pre>
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So if we print the content of the file in our command-line, the output will be the following:
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<pre>
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cat hello.txt
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Sun
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</pre>
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If we want to append a certain output to an existing file,
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we just have to use ">>" symbols:
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<pre>
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cat hello.txt
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Sun
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echo "Moon" >> hello.txt
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cat hello.txt
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Sun
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Moon
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</pre>
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<!-- Input redirection text -->
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<h3>input as output</h3>
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<br>
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To redirect an input from a file for a command, the symbol "<" is used.
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<pre>
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echo $lt; $(cat hello.txt)
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Sun
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Moon
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</pre>
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This is particularly useful when chaining commands.<br>
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<!-- Chaining command text -->
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<h3>Chaining (or piping)</h3>
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Chaining, also called Piping because it works with the pipe symbol "|", takes
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the output of a certain command-line and feeds it to another command in a direct way.
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<pre>
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cat hello.txt | grep Mo
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Moon
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</pre>
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<h3>A simple example</h3>
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Now let's say that we want to combine those commands in a more complex operation.
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Let's say we want to take some contents from a certain file and put it into another file.<br>
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We want to sort the animals whose name begins with letter "d" from the file
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<i>animals.txt</i> and put it into <i>d_animals.txt</i>.<br>
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<pre>
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grep d < animals.txt > d_animals.txt
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cat d_animals.txt
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Deer
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Dog
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Dolphin
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...
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</pre>
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