EXECV(3) | Library Functions Manual | EXECV(3) |
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[]);
This 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 these functions return, an error has occurred. The return value is -1, and the global variable errno will be set to indicate the error.
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).
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.
August 11, 2019 | OpenBSD-current |