EXEC(3) | Library Functions Manual | EXEC(3) |
execl
, execlp
,
execlpe
, execle
,
exect
, execv
,
execvp
, execvpe
—
#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[]);
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
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)).
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.
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.
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).
execl
(), execv
(),
execle
(), execlp
(), and
execvp
() conform to IEEE Std
1003.1-1990 (“POSIX.1”).
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.
September 1, 2019 | NetBSD 9.2 |