README.md

Bash Scripting

Resources

• Chmod Calculator

We start by creating a file with the .sh extension. For example script.sh. Then we write the script in it. For example:

Basic Script

#!/bin/bash

echo "Hello World"

We can run this by bash script.sh or ./script.sh. But the second will only work if the script is executable (permission to execute). We can make it executable by chmod +x script.sh. Now we can run it by ./script.sh.

Shebang

The first line of a bash script is called the shebang. It tells the system which interpreter to use to run the script. The shebang for bash is #!/bin/bash. The shebang for python is #!/usr/bin/env python. It vary from the langauge to language.

Variables

It is placeholder for a value. Just like any other programming language. We use $ to access the variable. Eg: $NAME. We can also use ${NAME}. The braces are used to make sure that the variable is not mistaken for a command.

#!/bin/bash

# Variable Declaration
NAME="John"

# Variable Usage

echo "My name is $NAME"
echo "My name is ${NAME}"

User Input

We can take input from the user using the read command.

#!/bin/bash

echo "Enter your name: "
read NAME
echo "Hello $NAME, nice to meet you!"

Arguments

We can pass arguments to the script. The arguments are stored in the $1, $2, $3 and so on. $0 is the name of the script.

Eg: bash script.sh arg1 arg2

#!/bin/bash

echo "First Argument: $1"

If Statement

#!/bin/bash

if [ "$1" == "John" ]
then
    echo "Hello John"
elif [ "$1" == "Doe" ]
then
    echo "Hello Doe"
else
    echo "I don't know you"
fi