EXEC(3) | Library Functions Manual | EXEC(3) |
execl
, execle
,
execlp
, execv
,
execvp
, execvP
—
execute a file
Standard C Library (libc, -lc)
#include
<unistd.h>
extern char **environ;
int
execl
(const char *path,
const char *arg0, ...,
/*, (char *)0,
*/);
int
execle
(const char *path,
const char *arg0, ...,
/* (char *)0 char *const
envp[] */);
int
execlp
(const char *file,
const char *arg0, ...,
/*, (char *)0,
*/);
int
execv
(const char *path,
char *const argv[]);
int
execvp
(const char *file,
char *const argv[]);
int
execvP
(const char *file,
const char *search_path, char *const
argv[]);
The exec
family of functions replaces 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(2) 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 *arg0 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 null-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
execvP
()
functions provide an array of pointers to null-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.
The
execle
()
function also specifies the environment of the executed process by following
the NULL
pointer that terminates the list of
arguments in the argument list or the pointer to the argv array with an
additional argument. This additional argument is an array of pointers to
null-terminated strings and must be terminated by a
NULL
pointer. 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
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. For
execlp
() and execvp
(),
search path is the path specified in the environment by
“PATH
” variable. If this variable is
not specified, the default path is set according to the
_PATH_DEFPATH
definition in
<paths.h>
, which is set to
“/usr/bin:/bin
”. For
execvP
(), the search path is specified as an
argument to the function. In addition, certain errors are treated
specially.
If an error is ambiguous (for simplicity, we shall
consider all errors except ENOEXEC
as being
ambiguous here, although only the critical error
EACCES
is really ambiguous), then these functions
will act as if they stat the file to determine whether the file exists and
has suitable execute permissions. If it does, they will return immediately
with the global variable errno restored to the value
set by
execve
().
Otherwise, the search will be continued. If the search completes without
performing a successful execve
() or terminating due
to an error, these functions will return with the global variable
errno set to EACCES
or
ENOENT
according to whether at least one file with
suitable execute permissions was found.
If the header of a file is not 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.)
If any of the exec
() functions returns, an
error will have occurred. The return value is -1, and the global variable
errno will be set to indicate the error.
Historically, the default path for the
execlp
() and execvp
()
functions was “:/bin:/usr/bin”. This
was changed to place the current directory last to enhance system
security.
The behavior of execlp
() and
execvp
() when errors occur while attempting to
execute the file is not quite historic practice, and 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 ETXTBSY
, upon which they retried
after sleeping for several seconds, and ENOMEM
and
E2BIG
, upon which they returned. They now return for
ETXTBSY
, and determine existence and executability
more carefully. In particular, EACCES
for
inaccessible directories in the path prefix is no longer confused with
EACCES
for files with unsuitable execute
permissions. In 4.4BSD, they returned upon all
errors except EACCES
,
ENOENT
, ENOEXEC
and
ETXTBSY
. This was inferior to the traditional error
handling, since it breaks the ignoring of errors for path prefixes and only
improves the handling of the unusual ambiguous error
EFAULT
and the unusual error
EIO
. The behaviour was changed to match the
behaviour of sh(1).
The execl
(),
execle
(), execlp
(),
execvp
(), and execvP
()
functions may fail and set errno for any of the errors
specified for the library functions
execve(2) and
malloc(3).
The execv
() function may fail and set
errno for any of the errors specified for the library
function execve(2).
The execl
(),
execv
(), execle
(),
execlp
(), and execvp
()
functions conform to IEEE Std 1003.1-1988
(“POSIX.1”). The execvP
()
function first appeared in FreeBSD 5.2.
January 24, 1994 | macOS 14.6 |