How to Run a Shell Script in Linux: 5 Best Ways

Written by

Ojash

Reviewed by

Akshat

Last updated: July 24, 2024

Expert verified

Do you find yourself repeatedly typing the same commands in Linux? There’s a solution: shell scripting. Imagine automating tasks with a simple text file! In this post, I’ll show you how to create scripts that automate tasks like backups, updates, and more. You’ll learn various methods to run scripts, handle files, and even troubleshoot common errors. Let’s explore simplify your Linux workflow!

What is a Shell Script?

A shell script is a simple text file containing a sequence of commands that you would normally enter manually into the command line of a Unix-based operating system like Linux. It’s a powerful tool for automating and simplifying tasks.

Purpose:

• Automation: Shell scripts automate repetitive tasks. Instead of typing the same commands every time, you can write them once in a script and run the script whenever needed. This saves time and reduces the chance of errors.
• Task Scheduling: Using tools like cron, you can schedule shell scripts to run at specific times or intervals. This is useful for tasks like backups, updates, or regular maintenance.
• Configuration Management: Shell scripts can set up and configure software systems quickly and consistently. They ensure that the configuration process is the same every time, which is crucial for maintaining stable and predictable systems.
• Batch Processing: Shell scripts can process multiple files or data sets in a single run. For example, you can write a script to resize all images in a directory or convert multiple video files to a different format.
• System Monitoring and Maintenance: Shell scripts can monitor system performance, check for errors, and perform routine maintenance tasks. For instance, they can check disk space and send an alert if it runs low.

Example:

Here’s a simple example of a shell script:

#!/bin/bash
# This is a comment
echo "Hello, World!" # This line prints "Hello, World!" to the terminal

How to Run a Shell Script in Linux [5 Simple Ways]

Now, let’s explore each method’s detailed steps here:

1. Run Shell Scripts Directly

This method involves executing shell script in Linux directly from the command line. Here’s what you need to do:

1. In the Terminal interface, create a script using the command

touch script_name.sh

2. Then, open this script with nano script_name.sh and add the following script to the file:

#!/bin/bash

# This is a sample shell script

echo "Hello, World!"
echo "This script demonstrates how to run a script in Linux."

# Additional commands and functionality can be added here

3. Save this script with Ctrl + O and then exit the Nano editor with Ctrl + X.

4. Use the command below to run the script, where script_name.sh will be the name of your shell script file.

./script_name.sh

5. Make the script executable with the command:

chmod +x script_name.sh

6. Your shell script will execute, and you’ll get the following output in the Terminal:

2. Use Shebang (#!/bin/bash)

Shebang is a special sequence of characters (#!/bin/bash) placed at the beginning of a shell script file. It specifies the interpreter to use when executing the script. Follow the steps below to run a shell script in Linux:

1. Open a text editor to create a new file for your shell script in Linux.

2. Add #!/bin/bash as the first line of the file, and add your script code below the shebang line.

#!/bin/bash
echo "This script demonstrates how to run a script in Linux with the Shebang notation."

3. Save the file with the .sh extension (e.g., script_name.sh).

4. Now, head to the Terminal and make the script executable using the command:

chmod +x script_name.sh

5. Execute the script in the Terminal by running:

./script_name.sh

6. The script will execute using the Bash interpreter specified in the shebang line and display the output in the Terminal.

3. Run Shell Scripts via Bash Command

This method involves using the bash command to execute shell scripts explicitly. Follow the steps below to use this method:

1. In the text editor, create a script file with the following content:

#!/bin/bash

echo "This script demonstrates how to run a script in Linux with the Bash command."

2. Execute the script using the command below, where script_name.sh is the name of your shell script file:

 bash script_name.sh

3. The script will run using the Bash interpreter, displaying the output in the Terminal.

4. Executing Shell Scripts Using Absolute Paths

In this method, you can execute shell scripts by specifying their absolute paths.

1. Use cd to navigate to the directory where your script file is saved, and determine the absolute path of your shell script using the command:

pwd

2. After that, make the script executable using the chmod command.

chmod +x scriptname.sh

3. Then, execute the script by running the following command, replacing /absolute/path/to/ with the actual path of your script:

/absolute/path/to/script_name.sh

4. Your script will execute using the specified absolute path and display the output in the Terminal.

5. Utilizing Environment Variables

Environment variables provide a way to pass information to shell scripts during execution. Let’s create a script that uses an environment variable to customize its behavior:

1. Open a text editor and write the following lines:

#!/bin/bash
echo "Welcome, $USERNAME!"

2. Save the file as welcome.sh and close it.

3. Now, head to the Terminal and set an environment variable by running (replace “Name” with your desired username):

export USERNAME="Name"

4. Make the script executable with the command:

chmod +x welcome.sh

4. Then, execute the script by running:

./welcome.sh

5. The script will execute and display a customized welcome message based on the value of the USERNAME environment variable.

4 Common Issues and Errors When Shell Scripting in Linux

Even with the best practices in place, shell scripting can sometimes encounter issues. In this section, I will discuss common problems and provide troubleshooting tips to help you overcome them.

• ⚙️ Syntax Errors: Syntax errors in shell scripts can hinder proper execution. To troubleshoot them, you should double-check command syntax, ensure the correct placement of quotes, parentheses, and special characters, use linting tools for error detection and suggestions, and comment out sections to isolate the problematic line.
• 🔒 Permission Denied Error: If you encounter a “Permission denied” error while executing a shell script, troubleshoot and resolve it by checking the file’s permissions using ls -l, granting execute permissions with chmod +x script_name.sh, and verifying correct ownership or group ownership.
• ❗️ Command Not Found Error: When facing a “Command not found” error, ensure the required command is installed on your system, use which command_name to locate the command’s path, and update the script accordingly. Also, check accessibility in the current environment and consider modifying the PATH variable.
• 🐞 Runtime Errors and Unexpected Output: If you encounter runtime errors or unexpected output during script execution, review error messages, implement error handling techniques like conditional statements and error codes, and debug the script using temporary echo statements or tools like set -x for tracing and identifying problematic code.

Wrapping Up

To wrap up, running shell scripts is pretty simple: create your script, make it executable, and run it. You can also use methods like shebang, running with the bash command, specifying absolute paths, and using environment variables. When you hit errors, check your script and use debugging tools.

For more learning, explore

• Explore debugging techniques with set -x in Bash to trace script execution and resolve issues effectively.
• Learn efficient methods for reading files line by line in Bash scripts, essential for handling large datasets and processing text files.
• Discover how to convert strings to numbers in Bash, crucial for numerical computations and data manipulation tasks in scripting.

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