I want to extract this number 156558 and put it in a variable abc

Then what are you waiting for? :P

A question for you ~ is array[0]=pppp_mmmm the 0th element of the array or are you trying to assign that whole string to the 0th element?

Update OPer updated his OP. -- If there will only be one period in the string than the regex that has been stated earlier will suffice. Could we get more sample data? (I assume that that is sample data and there are other strings that you need to retrieve information from.)