mini echo using rust

Getting started with Rust

Just follow the instructions on rust-lang.com and install the latest version of rust.

I am going to use the new RustRover by JetBrains for this blog but you can use any IDE you like.

Understanding the dir tree

If you are using cargo you can create a new project using

bash

cargo new recho --bin

the bin flag tells cargo that the program is a binary instead of a lib for which you use –lib. We will come back to lib in later blogs.

Here is the dir tree

.
├── Cargo.lock
├── Cargo.toml
├── src
│   └── main.rs

echo echo

One of the most important tasks of echo is to print the stdin to console.It has many other important tasks like previewing a cmd especially something like rm -rf * It can tell you about some variable like $ROS_SERVER and much more.
However today I am going to focus on just the simple printing of stdin to console.

Strings unattached

If you have worked with any programming language you would have guessed that we are going to work with strings today.
How rust handles strings is completely different than something like python, infact if you have not used a language with types (talking about you javascript) you might feel lost…
But we must march ahead. To access args you can use this

rust

fn main() {
    let args = env::args().collect();
    println!("{}", echo_input(args))
}

We define main function like in C. Then we use let (happy javascript noises) to define variable args. To insert type simply use ‘:’ and you can insert your desired type.
env::args().collect() will allow you to get the input in terms of ‘Vec‘.
Rust does not have classes so “::” allows access to a iterator inside module called args(We will come back to this later).
Based on the ‘trait’ you can perform multiple operations.
.collect() here will convert each iterated element to a Vector storing each of them as ‘String’.

Arguments (No one likes arguing)

Args are a good way to get user input in any program
Rust simply takes in the input you attach to your binary for example

bash

cargo run recho Args Kwargs Bargs

Rust will allow you to access Args Kwargs Bargs
as an element inside a Vector with type Vec<String>

Understanding rust args

The very first element of the args is ususally the path of the executable however it can be gibberish.To conclude conside the first element as rubbish and ignore it.The other elements are as per the input Args Kwargs Bargs.
The next thing to do is to print the input.To do this I have passed the input to another function (for testing)

Actual echo fn

rust

fn echo_input(args: Vec<String>) -> String {
    let mut output=String::new();
    for i in 1.. args.len(){
        let input:&String=&args[i];
        output.push_str(input);
        if i!=args.len()-1{
            output.push_str(" ")
        }
    }
    return output;
}

-> will allow you to define a type for the ‘return’ value.In this case it is a String.
let mut output=String::new() allows you to define a mutable variable as new empty String.
for i in 1.. args.len() will iterate from 1 to args.len().
let input:&String=&args[i] allows you to define another variable however you will see a new symbol here ‘&’(Happy C and C++ noises).This is called referencing. Rust works on the concept of borrowing once you tell rust that a=b you can not use b later because b now belongs to a.By using & you tell rust that to access the value it can just go to the location of where b is stored in this case args[i].
output.push_str(input) will concatenate the string to the output string.
Finally I want a whitespace after every element in args so i just concatenate a whitespace except for the last element.

Running the program

To run the program use

bash

cargo run -r Args Kwargs Bargs

It works!

bash

➜  recho git:(recho-bringup) ✗ cargo run -r Args Kwargs Bargs
   Compiling recho v0.1.0 (/home/thedevmanek/Documents/rust-mini-projects/recho)
    Finished `release` profile [optimized] target(s) in 0.15s
     Running `target/release/recho Args Kwargs Bargs`
Args Kwargs Bargs

However if you run

bash

cargo run -r 

Do you get an error?…

In the next blog we will write some tests to confirm that our code works in different cases till then Ciao!