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NAME
execl, execlp, execle, execv, execvp, execvpe - execute a file
LIBRARY
Standard C library (libc, -lc)
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 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 NOTES 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.
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).
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 │
└───────────────────────────────────────────────────────────┴───────────────┴─────────────┘
VERSIONS
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.
STANDARDS
environ
execl()
execlp()
execle()
execv()
execvp()
POSIX.1-2008.
execvpe()
GNU.
HISTORY
environ
execl()
execlp()
execle()
execv()
execvp()
POSIX.1-2001.
execvpe()
glibc 2.11.
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)