Exec (operating system)

In computing, exec is a functionality of an operating system that runs an executable file in the context of an already existing process, replacing the previous executable. This act is also referred to as an overlay. It is especially important in Unix-like systems, although exists elsewhere. As a new process is not created, the process identifier (PID) does not change, but the machine code, data, heap, and stack of the process are replaced by those of the new program.

The exec is available for many programming languages including compilable languages and some scripting languages. In OS command interpreters, the exec built-in command replaces the shell process with the specified program.

Interfaces to exec and its implementations vary. Depending on programming language it may be accessible via one or more functions, and depending on operating system it may be represented with one or more actual system calls. For this reason exec is sometimes described as a collection of functions.

Standard names of such functions in C are execl, execle, execlp, execv, execve, and execvp (see below), but not "exec" itself. Linux kernel has one corresponding system call named "execve", whereas all aforementioned functions are user-space wrappers around it.

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