How to Write Shell Scripts in Linux

Shell scripting makes it easy to automate tasks in Linux by letting you write and run a series of commands in one go.

Scripting saves time by automating repetitive commands, making daily tasks easier and even allowing scheduled execution. You can also run scripts at startup to display messages or set environment variables. There are countless uses—so let’s dive in!

In this guide, you’ll learn:

• What the Bash shell is.
• What Bash scripts are and how to recognize them.
• How to create and run your first Bash script.
• The basics of shell scripting.
• How to check scheduled scripts on your system.
• How to automate tasks with cron jobs.

Introduction to the Bash Shell

The Linux command line runs through a program called the shell, which has evolved over time with different options.

Most users stick with the default shell, which on many Linux distros is Bash (GNU Bourne-Again Shell), a successor to the Bourne shell (sh).

When you start the shell, it loads settings from a startup script in the .bashrc or .bash_profile file, letting you customize how it works.

When you’re using a shell interactively, you’ll see a $ symbol whenever it’s ready for your command. This is called the shell prompt.

[username@host ~]$

If you’re logged in as root, the prompt changes to #.

root@local:~#

Bash is a powerful tool that makes complex tasks much easier compared to using a graphical interface. Since most servers don’t have a GUI, learning to use the command line can be a huge advantage.

What is a Bash Script?

A Bash script is simply a file containing a series of commands that Bash executes line by line. Instead of typing commands manually every time, you can save them in a script and run it whenever needed. For example, you could navigate to a folder, create a new directory, and start a process—all in one go. Running the script automates these steps, making it easy to repeat as many times as you want.

You can recognize a Bash script in two main ways:

1. File Extension (.sh) – Many Bash scripts end with .sh, but it’s not required. They can run just fine without it.
2. Shebang (#!) – The first line of a Bash script usually starts with #!/bin/bash. This tells the system to run the script using the Bash shell.

That’s it! Even without the .sh extension, as long as the script has the right shebang and execute permissions, it will work.

Below is an example of the shebang

#! /bin/bash

Find the path to your bash shell.

# which bash

Check the current shell

# echo $SHELL

How to Create Your First Bash Script

# vim test.sh
#!/bin/bash
echo "Hello World"

Give your user permission to run the script by using this command:

# chmod +x test.sh

You can run the script in the following ways:

# bash test.sh

# ./test.sh

Set a variable using variable_name=value, and get its value with $variable_name.

# vim variable.sh
#!/bin/bash
# A simple variable example
greeting=Hello
name=bitscentric.com
echo "$greeting $name Team!"

Run the script

# bash variable.sh

Sometimes, you need to get input from the user and take action based on it.

Addition of two number using shell script

# vim sum.sh
#!/bin/bash
echo "Enter 1st numner->"
read a

echo "Enter 2nd numner->"
read b

var=$((a+b))
echo "Sum of $a and $b =$var"

# bash sum.sh

Loop in script

For loop

Create a loop script will run ten times.

# vim loop.sh
#!/bin/bash

for i in {1..10}
do
    echo $i
done

Run the script

# bash loop.sh

Table of any number script

# vim table.sh

#!/bin/bash
echo "Enter any postive number for table->"
read n
echo "Table of $n"
for i in {1..10}
do
        echo $i*$n=$(($i*$n))
done

Run the script

# bash table.sh

Create a loop shell script for string

# vim string_loop.sh

#!/bin/bash

for i in Hello! bitscentric.com Team.
do
    echo $i
done

Run the script

# bash string_loop.sh

While loop

A while loop runs as long as its condition is true. To control it, we need to update a counter inside the loop.

Example while loop, the counter statement that increments the value

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

Run the script

#  bash while.sh