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 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 name of a file that is to be
executed.
The functions can be grouped based on the letters following the "exec"
prefix.
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.
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.
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.
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.
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)