Chek Format from textbox

hi, i want to chek the Format of strings . e.g i have two format  'add $t1,$t5,$t4', 'addi $t1,$t1,20' how do i chek this format from text box when user input in textbox???. either i have to fix the string formats ?? but strng.Format() method are for numeric type what should i have to do for this type of data ??/plz help me in this 

Thanks