The
exec
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 function
execve(2).
(See the manual page for
execve()
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
"constchar *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();
and
execvp();
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();
function also specifies 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();
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.
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()
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()
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.)
RETURN VALUES
If any of the
exec
functions return, an error has occurred.
The return value is \-1, and the global variable
errno
will be set to indicate the error.
FILES
/bin/sh
default shell program
ERRORS
execl();,
execle();,
execlp();,
and
execvp();
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