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
ERRORS
execl
(), 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 ALSO
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.1”).