Originally Posted by man execl

execl(<shell path>, arg0, file, arg1, ..., (char *)0);

where <shell path> is an unspecified pathname for the sh utility, file is the process image file, and for execvp(), where arg0, arg1, and so on correspond to the values passed to execvp() in argv[0], argv[1], and so on.

The arguments represented by arg0,... are pointers to null-terminated character strings. These strings shall constitute the argument list available to the new process image. The list is terminated by a null pointer. The argument arg0 should point to a filename that is associated with the process being started by one of the exec functions.

The argument argv is an array of character pointers to null-terminated strings. The application shall ensure that the last member of this array is a null pointer. These strings shall constitute the argument list available to the new process image. The value in argv[0] should point to a filename that is associated with the process being started by one of the exec functions.

The argument envp is an array of character pointers to null-terminated strings. These strings shall constitute the environment for the new process image. The envp array is terminated by a null pointer.

For those forms not containing an envp pointer ( execl(), execv(), execlp(), and execvp()), the environment for the new process image shall be taken from the external variable environ in the calling process.

The number of bytes available for the new process' combined argument and environment lists is {ARG_MAX}. It is implementation-defined whether null terminators, pointers, and/or any alignment bytes are included in this total.