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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | VERSIONS | STANDARDS | HISTORY | BUGS | SEE ALSO | COLOPHON |
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exec(3) Library Functions Manual exec(3)
execl, execlp, execle, execv, execvp, execvpe - execute a file
Standard C library (libc, -lc)
#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
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 new process image 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 VERSIONS for further details.
execvpe() searches for the program using the value of PATH from
the caller's environment, not from the envp argument.
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.
The exec() functions return only if an error has occurred. The
return value is -1, and errno is set to indicate the error.
All of these functions may fail and set errno for any of the
errors specified for execve(2).
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 │
└─────────────────────────────────┴───────────────┴─────────────┘
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.
environ
execl()
execlp()
execle()
execv()
execvp()
POSIX.1-2008.
execvpe()
GNU.
environ
execl()
execlp()
execle()
execv()
execvp()
POSIX.1-2001.
execvpe()
glibc 2.11.
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.
sh(1), execve(2), execveat(2), fork(2), ptrace(2), fexecve(3),
system(3), environ(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.9.1.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.9.1 2024-06-16 exec(3)
Pages that refer to this page: pmlogger(1), watch(1), xargs(1), execve(2), getpid(2), ptrace(2), seccomp(2), statfs(2), vfork(2), atexit(3), clearenv(3), confstr(3), glob(3), libexpect(3), lttng-ust(3), on_exit(3), pam_getenvlist(3), posix_spawn(3), statvfs(3), stdin(3), sysconf(3), system(3), systemd.exec(5), environ(7), signal-safety(7)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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