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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON |
EXEC(3) Linux Programmer's Manual EXEC(3)
execl, execlp, execle, execv, execvp, execvpe - execute a file
#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 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.
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).
The execvpe() function first appeared in glibc 2.11.
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 │
└──────────────────────────────┴───────────────┴─────────────┘
POSIX.1-2001, POSIX.1-2008.
The execvpe() function is a GNU extension.
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.
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 release 5.08 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/.
GNU 2019-08-02 EXEC(3)
Pages that refer to this page: pam_getenvlist(3) , signal-safety(7)
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