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I am glad that the following is available in the
TUHS
Research Unix archive.
The source code was released by Alcatel-Lucent with a
Statement Regarding Research Unix Editions 8, 9, and 10 about non-commercial usage.
Here is a rendering from 8th edition /usr/man/man2/exec.2
with some arbitrary emphasis in bold face.
EXEC(2) System Calls Manual EXEC(2) NAME execl, execv, execle, execve, execlp, execvp, exec, exece, environ - execute a file SYNOPSIS execl(name, arg0, arg1, ..., argn, 0) char *name, *arg0, *arg1, ..., *argn; execv(name, argv) char *name, *argv[]; execle(name, arg0, arg1, ..., argn, 0, envp) char *name, *arg0, *arg1, ..., *argn, *envp[]; execve(name, argv, envp) char *name, *argv[], *envp[]; extern char **environ; DESCRIPTION Exec in all its forms overlays the calling process with the named file, then transfers to the entry point of the core image of the file. There can be no return from a successful exec; the calling core image is lost. Files remain open across exec unless explicit arrangement has been made; see ioctl(2). Ignored/held signals remain ignored/held across these calls, but signals that are caught (see signal(2)) are reset to their default values. Each user has a real user ID and group ID and an effective user ID and group ID. The real ID identifies the person using the system; the effective ID determines his access privileges. Exec changes the effec- tive 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 name argument is a pointer to the name of the file to be executed. If the first two bytes of that file are the ASCII string `#!', then the first line of the file is taken to be ASCII and determines the name of the program to execute. The first nonblank string following `#!' in that line is substituted for name. Any second string, separated from the first by blanks or tabs, is inserted between the first two argu- ments (arguments 0 and 1) passed to the invoked file. The argument pointers arg0, arg1, ... or the pointers in argv address null-terminated strings. Conventionally argument 0 is the name of the file. Execl is useful when a known file with known arguments is being called; the arguments to execl are the character strings constituting the file and the arguments. A 0 argument must end the argument list. Execv is useful when the number of arguments is unknown in advance; the arguments to execv are the name of the file to be executed and a vector of strings containing the arguments. The last argument string must be followed by a 0 pointer. When a C program is executed, it is called as follows: main(argc, argv, envp) int argc; char **argv, **envp; where argc is the argument count and argv is an array of character pointers to the arguments themselves. As indicated, argc is conven- tionally at least one and the first member of the array points to a string containing the name of the file. Argv is directly usable in another execv because argv[argc] is 0. Envp is a pointer to an array of strings that constitute the environ- ment of the process. Each string consists of a name, a `=', and a null-terminated value; or a name, a pair of parentheses (), a value bracketed by { and }, and by a null. The array of pointers is termi- nated 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(5) for some conventionally used names. The C run-time start-off routine places a copy of envp in the global cell environ, which is used by execv and execl to pass the environment to any subprograms executed by the current program. The exec routines use lower-level routines as follows to pass an environment explicitly: execve(file, argv, environ); execle(file, arg0, arg1, . . . , argn, 0, environ); Execlp and execvp are called with the same arguments as execl and execv, but duplicate the shell's actions in searching for an executable file in a list of directories. The directory list is obtained from the environment. Exect is the same as execve, except it arranges for a stop to occur on the first instruction of the new core image for the benefit of tracers, see proc(4). FILES /bin/sh shell, invoked if command file found by execlp or execvp SEE ALSO fork(2), environ(5) DIAGNOSTICS If the file cannot be found, if it is not executable, if it does not start with a valid magic number (see a.out(5)), if maximum memory is exceeded, or if the arguments require too much space, a return consti- tutes the diagnostic; the return value is -1. Even for the super-user, at least one of the execute-permission bits must be set for a file to be executed. BUGS If execvp is called to execute a file that turns out to be a shell com- mand file, and if it is impossible to execute the shell, the values of argv[0] and argv[-1] will be modified before return. The path search of execlp and execvp does not extend to names substi- tuted by `#!'. EXEC(2)