PHP date availability checker

[illuminiphoto]

I would like a web page to display a text box where the user types in a date (dd/mm/yy) and submit button. The code then needs to search a text file for the date inputted and if in the text file the same web page displays 'congratulation' , if no date in text file the user inputted then displays 'sorry'.

Please could anybody help me with such a script?

Thanks in advance for any help someone can give.