Lesson 1

In the earlier modules of this course, you explored what shells are, how different shells compare, and why shell scripting remains a foundational skill in Unix and Linux environments. Up to this point, however, you have not yet written or executed a script of your own.

This module marks the transition from theory to practice. You will begin by creating a simple shell script, learning what distinguishes a script file from an ordinary text file, and understanding how the shell interprets and executes scripted commands.

By the end of this module, you will be able to:

1. Identify the characteristics that make a text file a valid shell script
2. Write output to the terminal using shell script commands
3. Accept user input from the keyboard within a script
4. Add comments to document and explain script behavior
5. Modify Unix file permissions to make a script executable
6. Execute a shell script from the command line

A shell script is a text file containing a sequence of commands written in a shell’s built-in scripting language. These commands are interpreted and executed by a shell process, rather than being compiled into machine code.

The shell itself is a program that provides a text-based user interface to the operating system. It reads commands entered at the command line (also called a terminal window), interprets them, and passes instructions to the operating system for execution.

On most modern Linux systems, the default shell is bash (the Bourne Again Shell). Bash, like other Unix shells, includes a full scripting language that supports variables, conditionals, loops, input/output, and command substitution. Scripts written in bash are widely portable across Unix-like operating systems.

One of the strengths of shell scripting is accessibility. Scripts are easy to create, easy to modify, and widely shared. Many administrative tasks, system startup routines, and maintenance jobs rely on shell scripts that are included by default with Unix and Linux distributions.

In the early days of personal computing, languages such as BASIC allowed users to write small programs directly on microcomputers. Shell scripting serves a similar role in modern Unix and Linux systems, enabling users with modest experience to automate tasks and experiment with system behavior.

Today’s environments range from large enterprise servers to compact single-board computers such as the Raspberry Pi. In all of these contexts, shell scripting provides a practical way to explore system capabilities, automate repetitive work, and prototype solutions quickly.

Shell scripts are often used as an early step in application development. Prototyping logic in a script allows you to validate workflows, identify limitations, and test assumptions before committing to more complex implementations in languages such as C, C++, Java, Perl, or Python.

This approach reflects the traditional Unix philosophy: solving complex problems by composing small, focused tools. Shell scripting encourages this mindset by allowing you to chain together simple utilities, each performing a specific task, into a cohesive and powerful solution.