cat.js

#!/usr/bin/env node

/* GNU utility `cat` as a JavaScript executable.
 *
 * This works mostly the same as `cat`, with one difference: an explicit
 * argument of '-' (specifying stdin) is processed _after_ all filename
 * arguments.
 *
 * USAGE: cat.js [<FILE> <FILE...> [-]]
*/

'use strict';
let fs = require('fs');


function readStdin() {
    process.stdin.on('readable', function() {
        let chunk = process.stdin.read();
        if (chunk !== null) {
            process.stdout.write(chunk);
        }
    });
}

if (!process.argv.slice(2).length) {
    readStdin();
}
process.argv.forEach(function(file, index) {
    if (index < 2) {
        return;
    }
    if (file == '-') {
        readStdin();
        return;
    }
    fs.readFile(file, 'utf8', function(error, data) {
        if (error) {
            throw new Error(
                `File "${file}" does not exist or is not readable`
            );
        }
        console.log(data);
    });
});