boredos_mirror/docs/appdev/examples/01_hello_cli.md

Example 01: Hello CLI

The absolute basics. Writing a terminal program.

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This example demonstrates the bare minimum structure of a BoredOS application that outputs text to the standard output (usually the Terminal executing the binary).

📝 Concepts Introduced

• Including stdlib.h for basic IO.
• The main() entry point.
• Using printf() for formatted output.

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💻 The Code (src/userland/cli/hello_world.c)

#include <stdlib.h>

int main(int argc, char **argv) {
    // Standard library initialization is handled automatically by crt0.asm
    
    // Print a simple string to the terminal
    printf("Hello, World from BoredOS Userland!\n");
    
    // Print some formatted data
    int favorite_number = 67;
    printf("Did you know my favorite number is %d?\n", favorite_number);
    
    // Returning from main automatically terminates the process cleanly
    return 0;
}

🛠️ How it Works

1. #include <stdlib.h>: We include the SDK's standard library header which gives us access to printf.
2. int main(...): Every process begins execution here (managed transparently by crt0.asm).
3. printf(...): The SDK routes this call internally directly to the SYS_WRITE system call, making it available on the terminal.
4. return 0: A successful exit code.

🚀 Running It

If you build the project, you can open the Terminal and type:

/ # hello_world
Hello, World from BoredOS Userland!
Did you know my favorite number is 67?
/ #