NAME
execl
, execlp
,
execlpe
, execle
,
exect
, execv
,
execvp
, execvpe
—
execute a file
LIBRARY
library “libc”
SYNOPSIS
#include
<unistd.h>
extern char **environ;
int
execl
(const
char *path, const char
*arg, ...);
int
execlp
(const
char *file, const char
*arg, ...);
int
execlpe
(const
char *path, const char
*arg, ...,
char *const envp[]);
int
execle
(const
char *path, const char
*arg, ...,
char *const envp[]);
int
exect
(const
char *path, char *const
argv[], 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[]);
DESCRIPTION
Theexec
()
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 script(7) manual page provides detailed information about the
execution of interpreter scripts.)
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
(), execlpe
(), 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
exect
(),
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.
The
execle
(),
execlpe
(),
exect
(), 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. 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
(),
execlpe
(),
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 the PATH
variable. If this variable isn't specified,
_PATH_DEFPATH from
<paths.h>
is used instead,
its value being:
/usr/bin:/bin:/usr/pkg/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 the file is currently busy (the attempted
execve(2) returned ETXTBUSY
), these functions
will sleep for several seconds, periodically re-attempting to execute the
file.
The function
exect
()
executes a file with the program tracing facilities enabled (see
ptrace(2)).
RETURN VALUES
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.
FILES
- /bin/sh
- The shell.
COMPATIBILITY
Historically, the default path for the
execlp
() execlpe
(),
execvp
(), and execvpe
()
functions was “:/bin:/usr/bin”. This
was changed to improve security and behaviour.
The behavior of execlp
(),
execlpe
(), execvp
(), and
execvpe
() 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
(),
execlpe
(), execvp
(), and
execvpe
() 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.
ERRORS
execl
(), execle
(),
execlp
(), execlpe
(),
execvp
(), and execvpe
() may
fail and set errno for any of the errors specified for
the library functions
execve(2) and
malloc(3).
exect
() and
execv
() may fail and set errno
for any of the errors specified for the library function
execve(2).
SEE ALSO
STANDARDS
execl
(), execv
(),
execle
(), execlp
(), and
execvp
() conform to IEEE Std
1003.1-1990 (“POSIX.1”).
HISTORY
The exec
() function appeared in
Version 1 AT&T UNIX. The
execlpe
() function appeared first in QNX and the
execvpe
() function exists on both
NetBSD and QNX.