Seed #2: Standard Input (stdin) and Standard Output (stdout)

Fundamental concepts of stream flow management in operating and development systems

Once, in a technical interview, the interviewer started the interview with this question: Do you know what standard input is? Do you know what standard output is?.

My brain at the time....

My answer was not very clear but I was somewhat right. My answer was “standard input is when you use the terminal to run commands like ls or when you use the python input function to read user input from the terminal.”.

What is Standard Input (stdin)?

Standard Input (stdin) is a stream of input data that a program can read. By default, stdin is the keyboard. Programs read data from stdin when they need to receive information from the user. In programming languages, this is handled by functions such as input() in Python, scanf() in C, cin in C++ and stdin() in Rust.

• Example in Python

  user_input = input("Enter your name: ")
  print(f"Hello, {user_input}!")

• Example in Rust

  

use std::io;

fn main() {
    println!("Enter your name:");

    let mut name = String::new();
    io::stdin()
        .read_line(&mut name)
        .expect("Failed to read line");

    println!("Hello, {}!", name.trim());
}

What is Standard Output (stdout)?

Standard Output (stdout) is a stream of output data that a program can write. By default, stdout is the terminal or console screen. Programs send data to stdout to display results to the user. This is done using functions such as print() in Python, printf() in C, cout in C++ and println! in Rust.

• Example in Python

  print("Hello, I am a standard output")

• Example in Rust

  fn main() {
      // Print a line with a newline at the end
      println!("Hello, World!");
  
      // Print without a newline at the end
      print!("Hello, ");
      print!("World!");
  }

---

Bonus!

Difference Between stdout and stderr

Standard Output (stdout) and Standard Error (stderr) are both output streams used in computing to handle output from programs, but they serve different purposes.

• stdout (Standard Output): This is the primary channel used by programs to output general information, such as results or regular output. Typically, stdout is displayed on the screen or redirected to a file.

• stderr (Standard Error): This is a separate channel used specifically for outputting error messages. This allows error messages to be kept separate from standard output, making it easier to debug programs and handle errors appropriately. Typically, stderr is displayed on the screen but can also be redirected independently from stdout.

Redirect the standard I/O

Stdin and stdout can be redirected to and from files or devices. This is useful for automation and management of data flows in scripts.

Example of redirection in a Unix/Linux terminal:

# Redirect stdout to a file
cargo run > stdout.txt

# Redirect stderr to a file
cargo run 2> stderr.txt

# Redirect both stdout and stderr to different files
cargo run > stdout.txt 2> stderr.txt

# Redirect both stdout and stderr to the same file
cargo run > all_output.txt 2>&1

Explanation

• > is used to redirect stdout.

• 2> is used to redirect stderr.

• 2>&1 is used to redirect stderr to the same destination as stdout.

References

• Wikipedia: Standard Streams

• Python Official Documentation: Built-in Functions - input()

• Cplusplus.com: Standard Input and Output

• Rust Official Documentation: Function std::io::stdin

• Introducción a Bash - STDIN, STDOUT, STDERR y concatenación de comandos

Follow The Senior IT on Instgram @theseniorit and Facebook Page The Senior It