How do i convert this Mod_rewrite rule to nginx

Question

This is the Htacces rule:

RewriteEngine on
RewriteRule ^([A-Za-z0-9-]+)/?$ ir.php?id=$1

how should I pass it to a Nginx compliant rewrite rule... i read the doc and did this:

rewrite ^([A-Za-z0-9-]+)/?$ ir.php?id=$1 last;

But didnt work. and another question: Is there any equivalent of .htaccess to Nginx (per directory rules) Thanks