In reply to Pooja.balachandran:
$time returns 1 value. But you are assigning this value to a 2-dim array.
You can write only a string to the file.
Reading back the data from the file you have to re-format this string.
Look here to see the details:
If you want to use an array (without file I/O) you need for each entry an array element. It might result in a huge array.