An interpreter file begins with a line of the form ``#! interpreter''. When an interpreter file is execve'd, the system execve's the specified interpreter, giving it the name of the originally exec'd file as an argument and shifting over the rest of the original arguments.
There can be no return from a successful execve because the calling core image is lost. This is the mechanism whereby different process images become active.
The argument argv is a null-terminated array of character pointers to null-terminated character strings. These strings constitute the argument list to be made available to the new process. By convention, at least one argument must be present in this array, and the first element of this array should be the name of the executed program (i.e., the last component of name).
The argument envp is also a null-terminated array of character pointers to null-terminated strings. These strings pass information to the new process that is not directly an argument to the command (see environ(7)).
Descriptors open in the calling process remain open in the new process, except for those for which the close-on-exec flag is set (see close(2)). Descriptors that remain open are unaffected by execve.
Ignored signals remain ignored across an execve, but signals that are caught are reset to their default values. Blocked signals remain blocked regardless of changes to the signal action. The signal stack is reset to be undefined (see sigvec(2) for more information).
Each process has real user and group IDs and an effective user and group IDs. The real ID identifies the person using the system; the effective ID determines his access privileges. Execve changes the effective user and group ID to the owner of the executed file if the file has the ``set-user-ID'' or ``set-group-ID'' modes. The real user ID is not affected.
The new process also inherits the following attributes from the calling process:
process ID see getpid(2) parent process ID see getppid(2) process group ID see getpgrp(2) access groups see getgroups(2) working directory see chdir(2) root directory see chroot(2) control terminal see tty(4) resource usages see getrusage(2) interval timers see getitimer(2) resource limits see getrlimit(2) file mode mask see umask(2) signal mask see sigvec(2), sigmask(2)
When the executed program begins, it is called as follows:
main(argc, argv, envp)
int argc;
char **argv, **envp;
where argc is the number of elements in argv (the ``arg count'') and argv is the array of character pointers to the arguments themselves.
Envp is a pointer to an array of strings that constitute the environment of the process. A pointer to this array is also stored in the global variable ``environ''. Each string consists of a name, an ``='', and a null-terminated value. The array of pointers is terminated by a null pointer. The shell sh(1) passes an environment entry for each global shell variable defined when the program is called. See environ(7) for some conventionally used names.