In markdown files, yaml syntax configuration contains Front-matter. Rmarkdown is one type markdown type used to generate reports with R language.

This tutorial tells how to add a current date in yaml formatter in rmarkdown files.

Suppose you have yaml front matter as follows

---
date: 2022-04-08T00:00:00-00:00
title: "YAML -  Current Date in rmarkdown"
output: html_document
author: Renuka
--- 

You want to replace the date field with the current date produced with the r expression.

IN R language, Sys.Date() returns the current date in yyyy-mm-dd

---
date: "`R Sys.Date()`"
title: "YAML -  Current Date in rmarkdown"
output: html_document
author: Renuka
--- 

Generates the

---
date: 2022-04-08
title: "YAML -  Current Date in rmarkdown"
output: html_document
author: Renuka
--- 

if you want different format in reports, You can use format function with desired format.

format(Sys.Date(), "%d-%m-%Y") - 16-07-2021
format(Sys.Date(), "%d %B %Y") - 16 July 2021

The same can be using the R format function in yaml syntax as below.

---
date: "`r format(Sys.Date(), "%d %B %Y")`"
title: "YAML -  Current Date in rmarkdown"
output: html_document
author: Renuka
--- 

Please note the R expression enclosed in ` quote that wrapped inside double quotes.