Basics of Linux Shell Scripting

Shell scripting is a text file with a list of commands that instruct an operating system that is run by UNIX shell which is a command line interpreter. Shell scripting helps to automate day-to-day manual tasks and reduce human intervention. This also helps to reduce human errors and time.

Note: Extension of shell script must be ".sh"

Let's look at the basic example

Steps

Create a new file and open the file
```
 vi echo.sh
```

Enter the following lines of code

 #!/bin/bash
 #Author: Tejal Girme
 #Date: 04/01/2024
 #Purpose: This script will print some statements on terminal

 echo "I will be a great DevOps Engineer"

Save the file
Esc + :wq

Here, the "echo" command will print "I will be a great DevOps Engineer" on the terminal.
Give execute permission to the file
```
 chmod 777 echo.sh
```
Execute a shell script

./echo.sh

What is `#!/bin/bash?` can we write `#!/bin/sh` as well?

#!/bin/bash tells the interpreter which shell should be used to execute the shell script
#!/bin/bash is called a shebang line

Yes, We can use either

#!/bin/bash

#!/bin/sh

Write a Shell Script which prints `I will complete #90DaysOofDevOps challenge`

#!/bin/bash
#Author: Tejal Girme
#Date: 04/01/2024
#Purpose: This script will print some statements on the terminal

echo "I will complete #90DaysOofDevOps challenge"

Write a Shell Script to take user input, input from arguments and print the variables

#!/bin/sh
#Author:Tejal Girme
#Date: 01/04/2024
#Purpose: This shell script will accept 2 Arguments from user and displays it

#Defining Variables
Arg1=$1
Arg2=$2

#Printing Variables
echo "First argument: $Arg1"
echo "Second argument: $Arg2"

Here
Arg1 --> Variable1
Arg2 --> Variable2

To Execute it

./input.sh tejal girme

and boom unfold the magic by running this command in the terminal.

Write an Example of If else in Shell Scripting by comparing 2 numbers.

#!/bin/sh
#Author: Tejal Girme
#Date: 01/04/2024
#Purpose: This shell script will compare 2 numbers using if else

#Defining Variables
Num1=8
Num2=10

#Comaring Variables
if [ $Num1 -lt $Num2 ]
then
        echo "$Num1 is greater than $Num2"
elif [ $Num1 -eq $Num2 ]
then
        echo "$Num1 is equal to $Num2"
else
        echo "$Num1 is lesser than $Num2"
fi

Happy Learning!!

Thanks For Reading! :)