1EXECL(3) Library Functions Manual EXECL(3)
2
6 execl, execv, execle, execlp, execvp, exec, execve, exect, environ -
7 execute a file
8
10 execl(name, arg0, arg1, ..., argn, 0)
11 char *name, *arg0, *arg1, ..., *argn;
12 execv(name, argv)
14 char *name, *argv[];
15 execle(name, arg0, arg1, ..., argn, 0, envp)
17 char *name, *arg0, *arg1, ..., *argn, *envp[];
18 exect(name, argv, envp)
20 char *name, *argv[], *envp[];
21 extern char **environ;
23
25 These routines provide various interfaces to the execve system call.
26 Refer to execve(2) for a description of their properties; only brief
27 descriptions are provided here.
28 Exec in all its forms overlays the calling process with the named file,
30 then transfers to the entry point of the core image of the file. There
31 can be no return from a successful exec; the calling core image is
32 lost.
33 The name argument is a pointer to the name of the file to be executed.
35 The pointers arg[0], arg[1] ... address null-terminated strings. Con‐
36 ventionally arg[0] is the name of the file.
37 Two interfaces are available. execl is useful when a known file with
39 known arguments is being called; the arguments to execl are the charac‐
40 ter strings constituting the file and the arguments; the first argument
41 is conventionally the same as the file name (or its last component). A
42 0 argument must end the argument list.
43 The execv version is useful when the number of arguments is unknown in
45 advance; the arguments to execv are the name of the file to be executed
46 and a vector of strings containing the arguments. The last argument
47 string must be followed by a 0 pointer.
48 The exect version is used when the executed file is to be manipulated
50 with ptrace(2). The program is forced to single step a single instruc‐
51 tion giving the parent an opportunity to manipulate its state. On the
52 VAX-11 this is done by setting the trace bit in the process status
53 longword. Exect is not available on the PDP-11.
54 When a C program is executed, it is called as follows:
56 main(argc, argv, envp)
58 int argc;
59 char **argv, **envp;
60 where argc is the argument count and argv is an array of character
62 pointers to the arguments themselves. As indicated, argc is conven‐
63 tionally at least one and the first member of the array points to a
64 string containing the name of the file.
65 Argv is directly usable in another execv because argv[argc] is 0.
67 Envp is a pointer to an array of strings that constitute the environ‐
69 ment of the process. Each string consists of a name, an “=”, and a
70 null-terminated value. The array of pointers is terminated by a null
71 pointer. The shell sh(1) passes an environment entry for each global
72 shell variable defined when the program is called. See environ(7) for
73 some conventionally used names. The C run-time start-off routine
74 places a copy of envp in the global cell environ, which is used by
75 execv and execl to pass the environment to any subprograms executed by
76 the current program.
77 Execlp and execvp are called with the same arguments as execl and
79 execv, but duplicate the shell's actions in searching for an executable
80 file in a list of directories. The directory list is obtained from the
81 environment.
82
84 /bin/sh shell, invoked if command file found by execlp or execvp
85
87 execve(2), fork(2), environ(7), csh(1)
88
90 If the file cannot be found, if it is not executable, if it does not
91 start with a valid magic number (see a.out(5)), if maximum memory is
92 exceeded, or if the arguments require too much space, a return consti‐
93 tutes the diagnostic; the return value is -1. Even for the super-user,
94 at least one of the execute-permission bits must be set for a file to
95 be executed.
96
98 If execvp is called to execute a file that turns out to be a shell com‐
99 mand file, and if it is impossible to execute the shell, the values of
100 argv[0] and argv[-1] will be modified before return.
1014.2 Berkeley Distribution August 4, 1987 EXECL(3)