NAME
execl,
execlp,
execle,
exect,
execv,
execvp
—
execute a file
LIBRARY
Standard C Library (libc, -lc)
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
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
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
sh(1),
execve(2),
fork(2),
ptrace(2),
environ(7),
script(7)
STANDARDS
execl(),
execv(),
execle(),
execlp(), and
execvp() conform to
IEEE Std 1003.1-1990
(“POSIX.1”).
The
execlpe() function appeared first in QNX and the
execvpe() function exists on both
NetBSD and QNX.