With the onset of the T+1 settlement cycle, the ex-date is the same as the record date. Investors who purchase shares any day before the ex-date will be documented as owners of shares on the record date. That means they'll be entitled to receive the benefit of rights issues. Investors who purchase shares on or after the ex-date won't be recognized as shareowners on the record date. Since India follows a T+1 settlement cycle, if you buy shares on the ex-date (i.e. record date), you will not hold the shares on the record date. Hence the shareholder will not be eligible for rights entitlement benefit if he buys the stock on ex-date.
To know more about Rights Issue, get the SEBI FAQs here, NSE FAQs here and BSE FAQs here.