EXEC
Section: Linux Programmer's Manual (3)
Updated: 2009-02-22
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NAME
execl, execlp, execle, execv, execvp - execute a file
SYNOPSIS
#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[]);
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
execve(2).
(See the manual page for
execve(2)
for further details about the replacement of the current process image.)
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 argument list or the
pointer to the
argv
array with an additional argument.
This additional
argument 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.
Special semantics for execlp() and execvp()
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)
failed with the error
EACCES),
these functions will continue searching the rest of the search path.
If no other file is found, however,
they will return with
errno
set to
EACCES.
If the header of a file isn't recognized (the attempted
execve(2)
failed with the error
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.)
RETURN VALUE
If any of the
exec()
functions returns, an error will have occurred.
The return value is -1, and
errno
will be set to indicate the error.
ERRORS
All of these functions may fail and set
errno
for any of the errors specified for the library function
execve(2).
CONFORMING TO
POSIX.1-2001.
NOTES
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.
SEE ALSO
sh(1),
execve(2),
fork(2),
ptrace(2),
fexecve(3),
environ(7)
COLOPHON
This page is part of release 3.27 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- Special semantics for execlp() and execvp()
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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