2.11BSD/man/cat3/execlp.0
EXECL(3) UNIX Programmer's Manual EXECL(3)
NAME
execl, execv, execle, execlp, execvp, exec, execve, exect,
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[];
exect(name, argv, envp)
char *name, *argv[], *envp[];
extern char **environ;
DESCRIPTION
These routines provide various interfaces to the _e_x_e_c_v_e sys-
tem call. Refer to _e_x_e_c_v_e(2) for a description of their
properties; only brief descriptions are provided here.
_E_x_e_c 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.
The _n_a_m_e argument is a pointer to the name of the file to be
executed. The pointers _a_r_g[_0], _a_r_g[_1] ... address null-
terminated strings. Conventionally _a_r_g[_0] is the name of
the file.
Two interfaces are available. _e_x_e_c_l is useful when a known
file with known arguments is being called; the arguments to
_e_x_e_c_l are the character strings constituting the file and
the arguments; the first argument is conventionally the same
as the file name (or its last component). A 0 argument must
end the argument list.
The _e_x_e_c_v version is useful when the number of arguments is
unknown in advance; the arguments to _e_x_e_c_v 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.
The _e_x_e_c_t version is used when the executed file is to be
manipulated with _p_t_r_a_c_e(2). The program is forced to single
step a single instruction giving the parent an opportunity
to manipulate its state. On the VAX-11 this is done by set-
ting the trace bit in the process status longword. _E_x_e_c_t is
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EXECL(3) UNIX Programmer's Manual EXECL(3)
not available on the PDP-11.
When a C program is executed, it is called as follows:
main(argc, argv, envp)
int argc;
char **argv, **envp;
where _a_r_g_c is the argument count and _a_r_g_v is an array of
character pointers to the arguments themselves. As indi-
cated, _a_r_g_c is conventionally at least one and the first
member of the array points to a string containing the name
of the file.
_A_r_g_v is directly usable in another _e_x_e_c_v because _a_r_g_v[_a_r_g_c]
is 0.
_E_n_v_p is a pointer to an array of strings that constitute the
_e_n_v_i_r_o_n_m_e_n_t of the process. Each string consists of a name,
an "=", and a null-terminated value. The array of pointers
is terminated by a null pointer. The shell _s_h(1) passes an
environment entry for each global shell variable defined
when the program is called. See _e_n_v_i_r_o_n(7) for some conven-
tionally used names. The C run-time start-off routine
places a copy of _e_n_v_p in the global cell _e_n_v_i_r_o_n, which is
used by _e_x_e_c_v and _e_x_e_c_l to pass the environment to any sub-
programs executed by the current program.
_E_x_e_c_l_p and _e_x_e_c_v_p are called with the same arguments as
_e_x_e_c_l and _e_x_e_c_v, 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.
FILES
/bin/sh shell, invoked if command file found by _e_x_e_c_l_p or
_e_x_e_c_v_p
SEE ALSO
execve(2), fork(2), environ(7), csh(1)
DIAGNOSTICS
If the file cannot be found, if it is not executable, if it
does not start with a valid magic number (see _a._o_u_t(5)), if
maximum memory is exceeded, or if the arguments require too
much space, a return constitutes 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 exe-
cuted.
BUGS
If _e_x_e_c_v_p is called to execute a file that turns out to be a
shell command file, and if it is impossible to execute the
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EXECL(3) UNIX Programmer's Manual EXECL(3)
shell, the values of _a_r_g_v[_0] and _a_r_g_v[-_1] will be modified
before return.
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