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Monday, 29 May 2017

Command line parameters in shell scripts


Command line parameters are a way to pass information into a program or script in order for it to do what you want it to. Some examples of command line parameters:

ls -l
cat textfile
The command line parameters here are the "-l" and "textfile"

How are command line parameters accessed within a shell script?
They are stored in these variables:
"$0":This holds the name of the command.
"$1":This holds the first parameter.
"$2":This holds the second parameter.
"$3":This holds the third parameter and the pattern repeats.
"$#":This holds the number of parameters that have been passed.
"$@":This holds all of the parameters

Lets make a simple script call it parameters.sh:
#!/bin/sh
echo "Name of script:$0"
echo "First parameter:$1"
echo "Second parameter:$2"
echo "Number of parameters:$#"
echo "All parameters:$@"
When we run the script you should get the following output
Input: 
sh parameters.sh hello world
Output:
Name of script:parameters.sh
First parameter:hello
Second parameter:world
Number of parameters:2
All parameters:hello world



How to format code within web pages


When displaying code within web pages it can be hard to read if it hasn't been separated from the other text and images on the page. To get around this problem I use the google code-prettify JavaScript.
This allows code to be displayed like this:
#!/bin/sh
echo "Hello, World!"

To implement this within your HTML you need to add the following lines of HTML:
At the start of your page:

<script src="https://cdn.rawgit.com/google/code-prettify
/master/loader/run_prettify.js"></script><script>

Then whenever you want to display code:

<pre class="prettyprint">
#!/bin/sh
echo "Hello, World!"
</pre>