const regex = /^(\/[^\/]*\/[^\/]*\/[^\/]*\/[^\/]*\/[^\/]*\/)[^\/]*(\/[^\/]*)/gm;
// Alternative syntax using RegExp constructor
// const regex = new RegExp('^(\\\/[^\\\/]*\\\/[^\\\/]*\\\/[^\\\/]*\\\/[^\\\/]*\\\/[^\\\/]*\\\/)[^\\\/]*(\\\/[^\\\/]*)', 'gm')
const str = `/v1/cp/members/XXXX/benefits/XXXXBG-XXXX-XXXX/benefitlist
/v1/cp/members/XXXX/benefits/XXXXBG-XXXX-XXXX-/excluded
/v1/cp/members/XXXX/benefits/XXXXUF-XXXX-XXXX-/benefitlist
/v1/cp/members/XXXX/benefits/XXXXUF-XXXX-XXXX-/excluded
/v1/cp/members/XXXX/benefits/XXXXUU-XXXX-XXXX-/benefitlist
/v1/cp/members/XXXX/benefits/XXXXUU-XXXX-XXXX-/excluded
/v1/cp/members/XXXX/benefits/XXXXXXXX-XXXX-XXXX-/benefitlist
/v1/cp/members/XXXX/benefits/XXXXXXXX-XXXX-XXXX-/excluded`;
const subst = `\1XXXX\2`;
// 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