Varnish JSESSIONID

sub vcl_hash {

    set req.hash += req.url;
    set req.hash += req.http.host;
  
    set req.http.X-Calc-Hash = "true";
  
    if( req.http.Cookie ~ "JSESSIONID" ) {
        set req.http.X-Varnish-Hashed-On =
            regsub( req.http.Cookie, "^.*?JSESSIONID=([a-zA-z0-9]{32}\.[a-zA-Z0-9]+)([\s$\n])*.*?$", "\1" );
        set req.hash += req.http.X-Varnish-Hashed-On;
    }
     
    return(hash);
}

Sorry, I don't understand, What does these lines?

Can you explain the PCRE part?

In case somebody stumbles upon this, Varnish has replaced req.hash with hash_data()

https://www.varnish-cache.org/docs/3.0/installation/upgrade.html#req-hash-is-replaced-with-hash-data

So this becomes

sub vcl_hash {
hash_data( req.url );
hash_data( req.http.host);
set req.http.X-Calc-Hash = "true";
if( req.http.Cookie ~ "JSESSIONID" ) {
set req.http.X-Varnish-Hashed-On = regsub( req.http.Cookie, "^.?JSESSIONID=([a-zA-z0-9]{32}.[a-zA-Z0-9]+)([\s$\n]).*?$", "\1" );
hash_data( req.http.X-Varnish-Hashed-On);
} return(hash); }