execl,
execlp,
execle,
execv,
execvp,
execvpe —
execute a file
#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[]);
int
execvpe(
const
char *file,
char
*const argv[],
char *const
envp[]);
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
execve(2) system call; see that
manual page 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(),
execvp() and
execvpe() 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() and
execvpe() functions also specify 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(),
execvp() and
execvpe() 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(2) 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(2) 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.)
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.
- /bin/sh
- default shell program
execl(),
execle(),
execlp(),
execvp(), and
execvpe() 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).
sh(1),
execve(2),
fork(2),
ktrace(2),
ptrace(2),
environ(7)
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.1”).
execvpe()
is a GNU extension.
The functions
execl() and
execv() first appeared in
Version 2 AT&T UNIX. A predecessor to
execvp(),
pexec(), first appeared in the Programmer's
Workbench (PWB/UNIX). The functions
execle(),
execlp(),
execve(), and
execvp() first appeared in
Version 7 AT&T UNIX.
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