EXEC(3) OpenBSD Programmer's Manual EXEC(3)NAME
execl, execlp, execle, execv, execvp - execute a file
SYNOPSIS
#include <unistd.h>
extern char **environ;
int
execl(const char *path, const char *arg, ...);
int
execlp(const char *file, const char *arg, ...);
int
execle(const char *path, const char *arg, ..., char *const envp[]);
int
execv(const char *path, char *const argv[]);
int
execvp(const char *file, char *const argv[]);
DESCRIPTION
The exec family of functions replace the current process image with a new
process image. The functions described in this manual page are front-
ends for the function execve(2). (See the manual page for execve for
detailed information about the replacement of the current process.)
The initial argument for these functions is the pathname of a file which
is to be executed.
The const char *arg and subsequent ellipses in the execl(), execlp(), and
execle() functions can be thought of as arg0, arg1, ..., argn. Together
they describe a list of one or more pointers to NUL-terminated strings
that represent the argument list available to the executed program. The
first argument, by convention, should point to the file name associated
with the file being executed. The list of arguments must be terminated
by a null pointer.
The execv() and execvp() functions provide an array of pointers to NUL-
terminated strings that represent the argument list available to the new
program. The first argument, by convention, should point to the file
name associated with the file being executed. The array of pointers must
be terminated by a null pointer itself.
The execle() function also specifies the environment of the executed
process by following the null pointer that terminates the list of
arguments in the parameter list or the pointer to the argv array with an
additional parameter. This additional parameter is an array of pointers
to NUL-terminated strings and must be terminated by a null pointer
itself. The other functions take the environment for the new process
image from the external variable environ in the current process.
Some of these functions have special semantics.
The functions execlp() and execvp() will duplicate the actions of the
shell in searching for an executable file if the specified file name does
not contain a slash (`/') character. The search path is the path
specified in the environment by PATH variable. If this variable isn't
specified, _PATH_DEFPATH from <paths.h> is used instead, its value being:
/usr/bin:/bin:/usr/sbin:/sbin:/usr/X11R6/bin:/usr/local/bin
In addition, certain errors are treated specially.
If permission is denied for a file (the attempted execve returned
EACCES), these functions will continue searching the rest of the search
path. If no other file is found, however, they will return with the
global variable errno set to EACCES.
If the header of a file isn't recognized (the attempted execve returned
ENOEXEC), these functions will execute the shell with the path of the
file as its first argument. (If this attempt fails, no further searching
is done.)
RETURN VALUES
If any of the exec functions return, an error has occurred. The return
value is -1, and the global variable errno will be set to indicate the
error.
FILES
/bin/sh default shell program
ERRORSexecl(), execle(), execlp(), and execvp() may fail and set errno for any
of the errors specified for the library functions execve(2) and
malloc(3).
execv() may fail and set errno for any of the errors specified for the
library function execve(2).
SEE ALSOsh(1), execve(2), fork(2), ktrace(2), ptrace(2), environ(7)STANDARDS
Historically, the default path for the execlp() and execvp() functions
was .:/bin:/usr/bin. This was changed to improve security and behaviour.
The behavior of execlp() and execvp() when errors occur while attempting
to execute the file is historic practice, but has not traditionally been
documented and is not specified by the POSIX standard.
Traditionally, the functions execlp() and execvp() ignored all errors
except for the ones described above and ENOMEM and E2BIG, upon which they
returned. They now return if any error other than the ones described
above occurs.
execl(), execv(), execle(), execlp() and execvp() conform to IEEE Std
1003.1-1988 (``POSIX'').
OpenBSD 4.9 May 31, 2007 OpenBSD 4.9