sass-duplicate-match.js

const fs = require('fs');

const fileContents = fs.readFileSync(process.argv[2]).toString();

const regex = /\$[A-Za-z\-]*:/g;

let matches;
let variables = [];

while ((matches = regex.exec(fileContents)) !== null) {
    const match = matches[0];

    if (variables.indexOf(match) > -1) {
        console.log(`Duplicate variable: ${match}`);
    } else {
        variables.push(match);
    }
}