1. A computer implemented method for a built-in function of a shell to execute in a thread of an interactive shell process, the method comprising: receiving a request to execute the built-in function, wherein the request is formatted with a trailing character as a thread creating indicator; determining that the request includes the thread creating indicator; scheduling the thread to execute the built-in function, in response to a determination that the request includes the thread creating indicator, wherein the thread is controlled by the interactive shell process and shares an environment of the interactive shell process; declaring a variable based on at least one instruction of the built-in function; accessing the variable, wherein the variable is in an environment controlled by the interactive shell process; determining that the variable is not associated with a local indicator; determining that variable is coded for access exclusively by the built-in function, wherein the step of accessing comprises locking the variable, in response to a determination that the variable is coded for access exclusively by the built-in function; and unlocking the variable prior to freeing the thread.