execl, execlp, execle, execv, execvp — 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) ; |
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 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 null-terminated strings
that represent the argument list available to the executed
program. The first argument, by convention, should point to
the filename associated with the file being executed. The
list of arguments must
be terminated by a NULL
pointer, and, since these are variadic functions, this
pointer must be cast (char *)
NULL.
The execv
() and execvp
() functions provide an array of
pointers to null-terminated strings that represent the
argument list available to the new program. The first
argument, by convention, should point to the filename
associated with the file being executed. The array of
pointers must
be
terminated by a NULL pointer.
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 null-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.
The functions execlp
() and
execvp
() will duplicate the
actions of the shell in searching for an executable file if
the specified filename 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, the default
path ``:/bin:/usr/bin'' is used. 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 (/bin/sh
) with the path of the file as its
first argument. (If this attempt fails, no further
searching is done.)
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.
All of these functions may fail and set errno
for any of the errors specified for
the library function execve(2).
On some other systems the default path (used when the
environment does not contain the variable PATH
) has the current working directory
listed after /bin
and
/usr/bin
, as an
anti-Trojan-horse measure. Linux uses here the traditional
"current directory first" default path.
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. BSD (and possibly other
systems) do an automatic sleep and retry if ETXTBSY is
encountered. Linux treats it as a hard error and returns
immediately.
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.
sh(1), execve(2), fork(2), ptrace(2), fexecve(3), environ(7)
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