= Hands-On =
== Linux programming (scripting) ==

Shell Scripting is the language of the linux terminal. Shell scripts are sometimes referred to as “shebang” which is derived from the “#!” notation. Shell scripts are executed by interpreters present in the linux kernel. Interpreters include: bash, csh, zsh e.t.c. Most popular of which is bash.
 Typical operations performed by shell scripts include file manipulation, program execution, and printing text.

How to Write Shell Script in Linux/Unix

- Create a file using a vi editor(or any other editor). Name script file with extension . sh.
- Start the script with #! /bin/sh.
- Write some code.
- Save the script file as filename.sh.
- For executing the script type bash filename.sh.

File Color : Executable scripts appear in a different colour from rest of the files and folders.

Let's start to have some experience on scripting

===== Simple Script for newbies =====

First we have to create a text file

`$cat > hello.sh`

And create the content in it

#!/bin/sh 
echo 'Hello World'

`#!/bin/sh` is "how to run" the program.
`echo 'Hello World'` is "what to do" in the script

Then make the file executable

`$ chmod +x hello.sh`

And run the executable file

`$./hello.sh`

Output:

Hello world

Make yourself familiar with `man man` and `man apropos` on the shell. It will need for your self-tutoring.

==== Let's make this little advanced ====

===== How to define variables =====

Variables can be defined using the syntax ` variable_name=value`. To get the value of the variable, add `$` before the variable

#!/bin/bash
# A simple variable example
greeting=Hello
name=world
echo $greeting $name

===== Arithmetic Expressions =====

These are the operstors supported by bash for mathematical calculations.

+	addition
-	subtraction
*	multiplication
/	division
**	exponentiation
%	modulus

Numerical expressions can also be calculated and stored in a variable using the syntax below:

`value=$((expression))`

#!/bin/bash

var=$((3+9))
echo $var

===== How to read user input =====

Sometimes user input are needed to perform relevant operations.

In bash, user inputs are taken using the` read` command.

`read variable_name`

To prompt the user with a custom message, use the `-p` flag.

`read -p "Enter your age" variable_name`

===== Numeric Comparison logical operators =====

Comparison is used to check if statements evaluate to true or false. 

Equality   	                num1 -eq num2	is num1 equal to num2
Greater than equal to	num1 -ge num2	is num1 greater than equal to num2
Greater than	                num1 -gt num2	is num1 greater than num2
Less than equal to	        num1 -le num2	is num1 less than equal to num2
Less than	                num1 -lt num2	is num1 less than num2
Not Equal to	                num1 -ne num2	is num1 not equal to num2

Syntax:

if [ conditions ]
    then
         commands
fi

===== Conditional Statements (Decision Making) =====

Conditions are expressions that evaluate to a boolean expression (true or false). To check conditions, we can use `if`,` if-else`,` if-elif-else` and nested conditionals.

===== Looping and skipping =====

For loops allow you to execute statements a specific number of times. 

Looping with numbers:

#!/bin/bash

for i in {1..5}
do
    echo $i
done

Looping with strings:

#!/bin/bash

for X in cyan magenta yellow  
do
	echo $X
done

====== While loop ======

While loops check for a condition and loop until the condition remains true. We need to provide a counter statement that increments the counter to control loop execution.

#!/bin/bash
i=1
while [[ $i -le 10 ]] ; do
   echo "$i"
  (( i += 1 ))
done

Reading files: 

Suppose we have a file sample_file.txt as shown below:

#!/bin/bash

LINE=1

while read -r CURRENT_LINE
	do
		echo "$LINE: $CURRENT_LINE"
    ((LINE++))
done < "sample_file.txt"



== Github administration ==

Creating a repository

Create a project directory and cd into it. Execute the following git command from the directory to create a git repository.

`git init`

==== Checking out a repository ====

You can create a copy of your git repository using the clone command. Execute the following command to clone your project directory.

`git clone /path/to/project-repository`

===== Every git repository has three trees. A working directory, Index and Head. ====

- Working directory: It contains the actual project files.

- Index: It is the staging area where you add the project files that needs to be committed.

- Head: Head is where the reference to you previous commit exists.

==== Adding file to the staging area: (add) ====

`git add <filename>`

Let’s say you want to add all the files in your project directory to the staging area. Execute the following command to do the same

`git add --all`

==== Committing new changes to the repository (commit): ====

Once you have added all the files to the staging area, you can commit the changes with a reference message using the “-m” flag as shown below.

git commit -m “my first commit” 

=== Using public git-hub packages (installing, upgrading) ===

=== Creating own private repository ===


There aren't any special steps required to create a private GitHub repository. They're exactly the same as if you were to create a standard GitHub repository, albeit with one difference: You click the radio button for the Private option