c0a6a75fce
git-svn-id: svn+ssh://atelier.inf.usi.ch/home/bevilj/group-1@280 a672b425-5310-4d7a-af5c-997e18724b81
96 lines
2.1 KiB
HTML
96 lines
2.1 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: variables defining deleting naming
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author: Dario Rasic
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title: Script Variables
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previous-page: pages/scripts/0-base-commands.html
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next-page: pages/scripts/2-special-variables.html
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---
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<!-- Intro -->
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A variable is simply a string to which we assign a certain type of data,
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which could be some text, a number, a filename or other types of data.<br>
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<!-- How to name a variable - text -->
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<h3>Naming a variable</h3>
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<!-- Explaination -->
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To name a variable in Unix we can only use letters, numbers or
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the underscore character (_).<br>
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Other characters can't be used because they have a special meaning in Unix Shell.<br>
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Some simple examples are:
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<pre>
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VAR_1
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VAR_2
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NAME_3
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name_4
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</pre>
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<!-- How to define a variable - text -->
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<h3>Defining a variable</h3>
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To define a certain variable, we use the following base case:
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<pre>
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variable_name=variable_value
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</pre>
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<!-- Examples of defining -->
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Let me show you a simple example:
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<pre>
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VAR_1=Strawberry
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</pre>
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<!-- How to access the variables - text -->
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To access a variable we have to use the dollar sign ($). So if I want to
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access VAR_1, I have to write:
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<!-- Examples of accessing -->
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<pre>
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VAR_1="Strawberry"
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echo $VAR_1
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Strawberry
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</pre>
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<!-- How to delete a variable - text -->
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<h3>Deleting a variable</h3>
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Deleting a variable means that the shell will remove a certain variable from the list of
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those that it tracks.<br>
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To delete a variable we use the following command:
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<pre>
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unset variable_name
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</pre>
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which in our case would be:
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<pre>
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unset VAR_1
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</pre>
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<!-- How to protect a variable - text -->
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<h3>Protecting variables</h3>
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To protect a certain variable, we can set it as read-only so that it can't be
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changed or deleted.<br>
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So, if we try to change the value of VAR_1, the result will be the following:
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<pre>
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VAR_1="Strawberry"
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readonly VAR_1
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VAR_1="Blueberry"
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VAR_1: This variable is read only.
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</pre>
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If we try to delete the variable, the shell will give us the following error:
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<pre>
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VAR_1="Strawberry"
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unset VAR_1
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VAR_1: This variable is read only.
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</pre>
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