Implementing ROT13 in Different Languages

ROT13 Implementations Across Languages

ROT13 is a classic programming exercise that reveals interesting differences between languages. Here are idiomatic implementations in several popular languages.

JavaScript

const rot13 = str => str.replace(/[a-zA-Z]/g, c =>
  String.fromCharCode(c.charCodeAt(0) + (c.toLowerCase() < 'n' ? 13 : -13))
);

This one-liner uses a regex to find letters and shifts them, choosing +13 or -13 based on whether the character is in the first or second half of the alphabet.

Python

import codecs
decoded = codecs.decode("Uryyb, Jbeyq!", "rot_13")
# "Hello, World!"

Python includes ROT13 as a built-in codec. For a manual implementation:

def rot13(text):
    return text.translate(str.maketrans(
        'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz',
        'NOPQRSTUVWXYZABCDEFGHIJKLMnopqrstuvwxyzabcdefghijklm'
    ))

Bash

echo "Hello, World!" | tr 'A-Za-z' 'N-ZA-Mn-za-m'
# Uryyb, Jbeyq!

The classic Unix approach using the tr (translate) command.

C

void rot13(char *str) {
    for (; *str; str++) {
        if ((*str >= 'A' && *str <= 'Z') || (*str >= 'a' && *str <= 'z')) {
            char base = (*str >= 'a') ? 'a' : 'A';
            *str = base + (*str - base + 13) % 26;
        }
    }
}

Go

func rot13(s string) string {
    return strings.Map(func(r rune) rune {
        switch {
        case r >= 'A' && r <= 'Z':
            return 'A' + (r-'A'+13)%26
        case r >= 'a' && r <= 'z':
            return 'a' + (r-'a'+13)%26
        default:
            return r
        }
    }, s)
}

Rust

fn rot13(input: &str) -> String {
    input.chars().map(|c| match c {
        'A'..='Z' => (b'A' + (c as u8 - b'A' + 13) % 26) as char,
        'a'..='z' => (b'a' + (c as u8 - b'a' + 13) % 26) as char,
        _ => c,
    }).collect()
}

Key Differences

• Python has ROT13 built into the standard library
• Bash achieves it with a single tr command
• JavaScript uses regex replace with a callback
• C/Go/Rust use explicit character arithmetic with modulo