Idea is to run the shell script or any OS command in the same shell as Parent perl script.

What do you mean by "in the same shell"? Perl programs don't run "in a shell". It maybe that their parent process is a shell, but that's not always the case. You cannot create another process that has the same parent as your parent, but you can use exec, which replaces the program you are currently running with another (and it's still the same program). If you want to continue the running program, you can fork, and then exec in the parent. This makes the "old" program a child of the "new" one, but the "new" one will have the shell (assuming the "old" one had a shell as its parent) as its parent.

I'm kind of curious what you are trying to achieve though.