waitpppoe.js

const exec = require('child_process').exec
const readline = require('readline');

const cmd = "ifconfig pppoe-wan |grep 'inet addr' |cut -d: -f2|awk '{print $1}'"
const ipPattern = /^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$/

function get_pppoe_ip() {
    return new Promise((resolve, reject) => {
        exec(cmd, (err, stdout, stderr) => {
            stdout = stdout.replace(/\n/g, "");

            if (err) {
                reject("error: " + err)
            }

            if (ipPattern.exec(stdout)) {
                resolve(stdout);
            } else {
                reject("");
            }
        });
    });
}

function sleep(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
}

(async () => {
    while (true) {
        try {
            let ip = await get_pppoe_ip();
            process.stdout.write(ip + "\n");
            process.exit(0);
        } catch (exception) {
        }

        await sleep(500);
    }
})();