Hello Rust

In PHP

php hello.php reads the file and runs it. There is no separate binary. Whatever echo prints is the program's output. OPcache can cache the opcodes so PHP does not re-parse every request, but you still ship and run source — there is no standalone binary sitting next to the file.

<?php

echo "Hello, Rust!\n";

In Rust

A Rust program needs a main function. println! writes a line to stdout. The ! means it is a macro, not a function. You can ignore that until macros have their own moment. The useful fact is that this file is not run directly.

fn main() {
    println!("Hello, Rust!");
}

rustc --edition 2024 hello.rs
./hello

On Windows the binary is hello.exe. rustc writes the executable next to the source file. That file is what you run.

The binary carries the standard library compiled in. There is no separate Rust runtime or interpreter to install on the machine that runs it. It only runs on the same OS and CPU target you compiled for (a Linux x86_64 binary will not run on macOS ARM, and so on). Cross-compiling is a later topic; for this course, build on the machine where you will run.

--edition 2024 matters when you invoke rustc yourself. Cargo puts the edition in Cargo.toml so you do not pass the flag each time.

Watch for: treating rustc hello.rs && ./hello as the normal workflow. It works for one file. The moment you want dependencies, tests, or fmt, you want Cargo.

Idiomatic Rust: fn main() is the entry point of a binary. There is no class and no framework.

Side by side

	PHP	Rust
Run the file	php hello.php	rustc writes a binary, then you run that
The process	The interpreter reads the source again	The binary is the program you run
Next step	Stay with the interpreter	cargo once you want dependencies or tests

Try it

Compile the file and run it. Then change the line to println!("Hello, {name}!"); and compile. rustc reports E0425 (cannot find value name). Then add let name = "Rust"; above it and compile again.

Key takeaways

• rustc produces a binary. PHP runs the source.
• Use Cargo for anything beyond a single file.

What's next: What is Cargo?