Introduction to Linux System Programming: Write Your First Hello World Program from Scratch

When we learn any programming language, the first program is often the classic “Hello World”. Linux system programming is no exception! Today, I will guide you step by step to complete your first program in a Linux environment and understand the principles behind it. (The following demonstration uses the Ubuntu 22.04 distribution)

🆚 Linux vs Windows: Comparison of Programming Environments

Steps	Windows Environment	Linux Environment
Create File	Create using VSCode GUI	Create using vi/gedit command line
Write Code	Write using VSCode editor	Write using terminal or text editor
Compile Code	Click compile button	Compile using command line
Run Program	Click run button	Run using command line

🚀 Getting Started: Create Your First Linux Program

Step 1: Create Source File

In Linux, we have multiple ways to create a source file:

Method 1: Using vi Editor (Recommended for Learning)

vi hello.c

Method 2: Using gedit GUI Editor

gedit hello.c

Step 2: Write Hello World Code

Enter the following code in the opened editor:

#include <stdio.h>

int main() {
    printf("Hello, World!\n");
    return 0;
}

Code Explanation:

• #include <stdio.h>: Includes the standard input-output library, allowing us to use theprintf function
• int main(): The main function of the program, which every C program must have
• printf("Hello, World!\n"): Prints “Hello, World!” on the screen,\n indicates a newline
• return 0: Tells the system that the program has ended normally

Step 3: Save File

• vi Editor: PressESC, type:wq, then press Enter
• gedit Editor: Click the save button or pressCtrl+S

🔧 Compile Program: From Source Code to Executable File

First, ensure that the GCC compiler is installed

sudo apt install gcc

What is GCC? GCC (GNU Compiler Collection) is a compiler that primarily converts high-level programming language source code into machine code. You can think of it as clicking the “compile” button in Windows, which actually executes the GCC command.

Compilation Method 1: One-Step (Recommended for Beginners)

gcc hello.c -o hello

Command Explanation:

• gcc: Calls the GCC compiler
• hello.c: The source file to be compiled
• -o hello: Specifies the output executable file name ashello

Compilation Method 2: Step-by-Step Compilation (Understanding the Compilation Process)

# Step 1: Compile to generate object file
gcc -c hello.c -o hello.o

# Step 2: Link object file to generate executable file
gcc hello.o -o hello

Step-by-Step Compilation Explained:

• gcc -c hello.c -o hello.o:

• -c: Tells GCC to only compile and assemble, not link
• hello.o: The generated object file

🤔 Why Use Step-by-Step Compilation?

Scenario Comparison:

Direct Compilation (suitable for single files):

gcc file1.c file2.c -o program

• Each modification requires recompiling all files, suitable for small projects

Step-by-Step Compilation (suitable for multi-file projects):

# First compile all files
gcc -c file1.c -o file1.o
gcc -c file2.c -o file2.o
gcc file1.o file2.o -o program

# If only file1.c is modified, just:
gcc -c file1.c -o file1.o  # Recompile the modified file
gcc file1.o file2.o -o program  # Relink

• Only recompiles modified files, saving time, suitable for large projects (of course, typing becomes cumbersome with many files, later we will use cmake for automatic compilation)

🎯 Run Your Program

After successful compilation, run the program:

./hello

You should see the output:

Hello, World!

Note: The preceding./ is important; it tells the system to look for the executable file in the current directory.

💡 Complete Process Demonstration

Let’s walk through the complete process in the terminal:

Introduction to Linux System Programming: Write Your First Hello World Program from Scratch — image-20251121180008699

# 1. Create source file
vi hello.c

# 2. Write the following code (press i in vi to enter edit mode, input code)

#include <stdio.h>
int main() {
    printf("Hello, World!\n");
    return 0;
}

# 3. Save and exit (press ESC, type :wq, press Enter)

# 4. Compile program
gcc hello.c -o hello

# 5. Run program
./hello

# 6. Check result
Hello, World!

🎉 Congratulations!

By now, you have successfully completed:

• ✅ Created a C program in a Linux environment
• ✅ Understood the principles of compilation
• ✅ Mastered the basic usage of the GCC compiler
• ✅ Run your first Linux program

Remember: Practicing hands-on is the best way to learn programming. Don’t be afraid of making mistakes; every error is an opportunity to learn!