The exec command replaces the current shell process with the specified command. Normally, when you run a command a new process is spawned (forked). The exec command does not spawn a new process. Instead, the current process is overlaid with the new command. In other words the exec command is executed in place of the current shell without creating a new process. The command implements Unix exec system call. It is a part of process control API, the group that also includes fork system call.