Exec

The  system call replaces the current process with a completely different process. This is commonly used in shells, servers, and any number of other types of software, where one program hands off execution to a different program.

A common proceedure is to " and  ". Here, a process will  to create a new "child" process with the same environment and settings as the "parent" (the original process). The child process will then  the new program and carry on execution.

Most command line shells use this proceedure for running programs.