G'day chandantul,

You should check perldiag when you encounter an error message that you don't understand. In this instance, "Modification of a read-only value attempted" describes a number of situations in which this particular message may be emitted.

If that information doesn't help, you should provide us with an SSCCE that reproduces your problem. In many cases, the process of writing an SSCCE will identify the problem for you. A single line of code, with no context, does not help us to help you.

Please also read: "How do I post a question effectively?".