EXEC
Section: Linux Programmer's Manual (3)
Updated: 2021-03-22
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NAME
execl, execlp, execle, execv, execvp, execvpe - execute a file
SYNOPSIS
#include <unistd.h>
extern char **environ;
int execl(const char *pathname, const char *arg, ...
/*, (char *) NULL */);
int execlp(const char *file, const char *arg, ...
/*, (char *) NULL */);
int execle(const char *pathname, const char *arg, ...
/*, (char *) NULL, char *const envp[] */);
int execv(const char *pathname, char *const argv[]);
int execvp(const char *file, char *const argv[]);
int execvpe(const char *file, char *const argv[], char *const envp[]);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
execvpe():
_GNU_SOURCE
DESCRIPTION
The
exec()
family of functions replaces the current process image with a new process
image.
The functions described in this manual page are layered on top of
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 name of a file that is
to be executed.
The functions can be grouped based on the letters following the "exec" prefix.
l - execl(), execlp(), execle()
The
const char *arg
and subsequent ellipses 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.
By contrast with the 'l' functions, the 'v' functions (below) specify the
command-line arguments of the executed program as a vector.
v - execv(), execvp(), execvpe()
The
char *const argv[]
argument is 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.
e - execle(), execvpe()
The environment of the caller is specified via the argument
envp.
The
envp
argument is an array of pointers to null-terminated strings and
must
be terminated by a null pointer.
All other
exec()
functions (which do not include 'e' in the suffix)
take the environment for the new process
image from the external variable
environ
in the calling process.
p - execlp(), execvp(), execvpe()
These functions duplicate the actions of the shell in
searching for an executable file
if the specified filename does not contain a slash (/) character.
The file is sought in the colon-separated list of directory pathnames
specified in the
PATH
environment variable.
If this variable isn't defined, the path list defaults to
a list that includes the directories returned by
confstr(_CS_PATH)
(which typically returns the value "/bin:/usr/bin")
and possibly also the current working directory;
see NOTES for further details.
If the specified filename includes a slash character, then
PATH
is ignored, and the file at the specified pathname is executed.
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.)
All other
exec()
functions (which do not include 'p' in the suffix)
take as their first argument a (relative or absolute) pathname
that identifies the program to be executed.
RETURN VALUE
The
exec()
functions return only if an error has occurred.
The return value is -1, and
errno
is set to indicate the error.
ERRORS
All of these functions may fail and set
errno
for any of the errors specified for
execve(2).
VERSIONS
The
execvpe()
function first appeared in glibc 2.11.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
Interface | Attribute | Value
|
execl(),
execle(),
execv()
| Thread safety | MT-Safe
|
execlp(),
execvp(),
execvpe()
| Thread safety | MT-Safe env
|
CONFORMING TO
POSIX.1-2001, POSIX.1-2008.
The
execvpe()
function is a GNU extension.
NOTES
The default search path (used when the environment
does not contain the variable PATH)
shows some variation across systems.
It generally includes
/bin
and
/usr/bin
(in that order) and may also include the current working directory.
On some other systems, the current working is included after
/bin
and
/usr/bin,
as an anti-Trojan-horse measure.
The glibc implementation long followed the traditional default where
the current working directory is included at the start of the search path.
However, some code refactoring during the development of glibc 2.24
caused the current working directory to be dropped altogether
from the default search path.
This accidental behavior change is considered mildly beneficial,
and won't be reverted.
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.
BUGS
Before glibc 2.24,
execl()
and
execle()
employed
realloc(3)
internally and were consequently not async-signal-safe,
in violation of the requirements of POSIX.1.
This was fixed in glibc 2.24.
Architecture-specific details
On sparc and sparc64,
execv()
is provided as a system call by the kernel
(with the prototype shown above)
for compatibility with SunOS.
This function is
not
employed by the
execv()
wrapper function on those architectures.
SEE ALSO
sh(1),
execve(2),
execveat(2),
fork(2),
ptrace(2),
fexecve(3),
system(3),
environ(7)
COLOPHON
This page is part of release 5.11 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- l - execl(), execlp(), execle()
-
- v - execv(), execvp(), execvpe()
-
- e - execle(), execvpe()
-
- p - execlp(), execvp(), execvpe()
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- ATTRIBUTES
-
- CONFORMING TO
-
- NOTES
-
- BUGS
-
- Architecture-specific details
-
- SEE ALSO
-
- COLOPHON
-
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Time: 06:22:46 GMT, May 09, 2021