const regex = /^app[0-9]+\s=\s\x22([0-9]+)\x22$/gm;
// Alternative syntax using RegExp constructor
// const regex = new RegExp('^app[0-9]+\\s=\\s\\x22([0-9]+)\\x22$', 'gm')
const str = `app1 = "0123456789"
app2 = "1234567890"
app3 = "2345678901"
app4 = "3456789012"
app5 = "4567890123"`;
const subst = `\1`;
// The substituted value will be contained in the result variable
const result = str.replace(regex, subst);
console.log('Substitution result: ', result);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions