A blog on BASH Scripting

<h1 align="center">Bash Scripting</h1>


BASH (Bourne Again Shell) is a command-line interpreter for shell scripts. It is widely used by many Unix and Linux distributions. BASH is an acronym for Bourne Again Shell. 

BASH is a shell script interpreter that is used to execute commands on Linux and other Unix-like operating systems. BASH is an acronym for Bourne Again Shell. 

BASH is a powerful scripting language that can be used to automate many tasks on a Linux or Unix system. In this blog post, we will explore some of the basics of BASH scripting. 

We will cover the following topics:

- Creating a BASH script
- Running a BASH script
- Basic BASH scripting constructs
- Loops in BASH
- Conditionals in BASH
- Functions in BASH
- Debugging BASH scripts

Let's get started!

Creating a BASH script

A BASH script is a text file that contains a list of commands to be executed by the BASH interpreter. To create a BASH script, simply create a new text file with the .sh extension. 

For example, let's create a simple script that prints the message "Hello, world!" to the screen. To do this, open a new text file in your favorite text editor and type the following:

#!/bin/bash

echo "Hello, world!"

Save the file and close the text editor. You have now created a BASH script!

Running a BASH script

To run a BASH script, simply type the path to the script file at the command prompt. 

For example, if the script file is saved in the current directory, you can run it by typing:

./hello_world.sh

If the script file is saved in a different directory, you will need to specify the full path to the script file. 

For example, if the script file is saved in the /home/user/scripts directory, you can run it by typing:

/home/user/scripts/hello_world.sh

Basic BASH scripting constructs

Now that we know how to create and run a BASH script, let's take a look at some of the basic scripting constructs. 

Comments

Comments are lines in a script that are not executed by the BASH interpreter. Comments are used to add notes or documentation to a script. Comments are prefixed with the # character. 

For example, the following script contains a comment:

#!/bin/bash

# This is a comment

echo "Hello, world!"

Variable assignment

Variables are used to store values in a script. Variables can be assigned using the = character. 

For example, the following script assigns the value "Hello, world!" to the variable message:

#!/bin/bash

message="Hello, world!"

echo $message

The echo command is used to print the value of a variable to the screen. 

Command substitution

Command substitution is used to execute a command and store the output in a variable. Command substitution is performed using the $(command) syntax. 

For example, the following script stores the output of the pwd (print working directory) command in the variable dir:

#!/bin/bash

dir=$(pwd)

echo $dir

If-then-else

The if-then-else construct is used to execute a set of commands based on a condition. The condition is evaluated using the test command. 

The general syntax of the if-then-else construct is as follows:

if test-command
then
   commands
else
   commands
fi

For example, the following script will print "Hello, world!" if the value of the variable message is "Hello, world!":

#!/bin/bash

message="Hello, world!"

if test $message = "Hello, world!"
then
   echo $message
else
   echo "The message is not Hello, world!"
fi

The test command can be used to evaluate many different types of conditions. For a complete list of the conditions that can be evaluated, please see the test(1) man page. 

Switch-case

The switch-case construct is used to execute a set of commands based on the value of a variable. The general syntax of the switch-case construct is as follows:

case variable in
pattern1)
   commands
   ;;
pattern2)
   commands
   ;;
*)
   commands
   ;;
esac

For example, the following script will print "Hello, world!" if the value of the variable message is "Hello, world!":

#!/bin/bash

message="Hello, world!"

case $message in
Hello, world!)
   echo $message
   ;;
*)
   echo "The message is not Hello, world!"
   ;;
esac

Loops in BASH

There are two types of loops in BASH: for and while. 

The for loop is used to execute a set of commands for each item in a list. The general syntax of the for loop is as follows:

for item in list
do
   commands
done

For example, the following script will print each item in the list:

#!/bin/bash

for item in 1 2 3 4 5
do
   echo $item
done

The while loop is used to execute a set of commands until a condition is met. The general syntax of the while loop is as follows:

while test-command
do
   commands
done

For example, the following script will print the numbers 1 through 5:

#!/bin/bash

i=1

while test $i -le 5
do
   echo $i
   i=$(($i + 1))
done

Conditionals in BASH

Conditionals are used to execute a set of commands based on a condition. The general syntax of the if-then-else construct is as follows:

if test-command
then
   commands
else
   commands
fi

For example, the following script will print "Hello, world!" if the value of the variable message is "Hello, world!":

#!/bin/bash

message="Hello, world!"

if test $message = "Hello, world!"
then
   echo $message
else
   echo "The message is not Hello, world!"
   fi

The test command can be used to evaluate many different types of conditions. For a complete list of the conditions that can be evaluated, please see the test(1) man page. 

Functions in BASH

Functions are used to group a set of commands together. Functions are declared using the function keyword. The general syntax of a function is as follows:

function function-name {
   commands
}

For example, the following script contains a function that prints the message "Hello, world!":

#!/bin/bash

function hello {
   echo "Hello, world!"
}

hello

Functions can also take arguments. The arguments are passed to the function using the $1, $2, $3, etc. variables. 

For example, the following script contains a function that prints the first argument that is passed to the function:

#!/bin/bash

function print_argument {
   echo $1
}

print_argument hello

Debugging BASH scripts

BASH scripts can be debugged using the -x and -v options. The -x option will print each command that is executed by the BASH interpreter. The -v option will print each command before it is executed. 

For example, the following script will print each command that is executed:

#!/bin/bash

# This is a comment

echo "Hello, world!"

To debug this script, simply type the following at the command prompt:

bash -x hello_world.sh

The output of the script will be as follows:

+ echo 'Hello, world!'
Hello, world!

The -x and -v options can be combined to print both the commands and the output of the commands. 

For example, the following script will print both the commands and the output of the commands:

#!/bin/bash

# This is a comment

echo "Hello, world!"

To debug this script, simply type the following at the command prompt:

bash -xv hello_world.sh

The output of the script will be as follows:

+ echo 'Hello, world!'
Hello, world!

That's it for this blog post! I hope you have learned some of the basics of BASH scripting.