EXEC(3) BSD Library Functions Manual EXEC(3)
execl, execlp, execle, exect, execv, execvp, execvP -- execute a file
Standard C Library (libc, -lc)
extern char **environ;
execl(const char *path, const char *arg, ... /*, (char *)0 */);
execlp(const char *file, const char *arg, ... /*, (char *)0 */);
execle(const char *path, const char *arg, ... /*, (char *)0, char *const envp */);
exect(const char *path, char *const argv, char *const envp);
execv(const char *path, char *const argv);
execvp(const char *file, char *const argv);
execvP(const char *file, const char *search_path, char *const argv);
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 the function execve(2). (See
the manual page for execve(2) for detailed information about the replacement of the current
The initial argument for these functions is the pathname of a file which is to be executed.
The const char *arg and subsequent ellipses in the execl(), execlp(), and execle() functions
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 exe-
cuted program. The first argument, by convention, should point to the file name associated
with the file being executed. The list of arguments must be terminated by a NULL pointer.
The exect(), execv(), execvp(), and execvP() functions provide 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 file name associated with the file being exe-
cuted. The array of pointers must be terminated by a NULL pointer.
The execle() and exect() functions also specify the environment of the executed process by
following the NULL pointer that terminates the list of arguments in the argument list or the
pointer to the argv array with an additional argument. This additional argument is an array
of pointers to null-terminated strings and must be terminated by a NULL pointer. The other
functions take the environment for the new process image from the external variable environ
in the current process.
Some of these functions have special semantics.
The functions execlp(), execvp(), and execvP() will duplicate the actions of the shell in
searching for an executable file if the specified file name does not contain a slash ``/''
character. For execlp() and execvp(), search path is the path specified in the environment
by ``PATH'' variable. If this variable is not specified, the default path is set according
to the _PATH_DEFPATH definition in <paths.h>, which is set to ``/usr/bin:/bin''. For
execvP(), the search path is specified as an argument to the function. In addition, certain
errors are treated specially.
If an error is ambiguous (for simplicity, we shall consider all errors except ENOEXEC as
being ambiguous here, although only the critical error EACCES is really ambiguous), then
these functions will act as if they stat the file to determine whether the file exists and
has suitable execute permissions. If it does, they will return immediately with the global
variable errno restored to the value set by execve(). Otherwise, the search will be contin-
ued. If the search completes without performing a successful execve() or terminating due to
an error, these functions will return with the global variable errno set to EACCES or ENOENT
according to whether at least one file with suitable execute permissions was found.
If the header of a file is not recognized (the attempted execve() returned ENOEXEC), these
functions will execute the shell with the path of the file as its first argument. (If this
attempt fails, no further searching is done.)
The function exect() executes a file with the program tracing facilities enabled (see
If any of the exec() functions returns, an error will have occurred. The return value is
-1, and the global variable errno will be set to indicate the error.
/bin/sh The shell.
Historically, the default path for the execlp() and execvp() functions was
``:/bin:/usr/bin''. This was changed to place the current directory last to enhance system
The behavior of execlp() and execvp() when errors occur while attempting to execute the file
is not quite historic practice, and has not traditionally been documented and is not speci-
fied by the POSIX standard.
Traditionally, the functions execlp() and execvp() ignored all errors except for the ones
described above and ETXTBSY, upon which they retried after sleeping for several seconds, and
ENOMEM and E2BIG, upon which they returned. They now return for ETXTBSY, and determine
existence and executability more carefully. In particular, EACCES for inaccessible directo-
ries in the path prefix is no longer confused with EACCES for files with unsuitable execute
permissions. In 4.4BSD, they returned upon all errors except EACCES, ENOENT, ENOEXEC and
ETXTBSY. This was inferior to the traditional error handling, since it breaks the ignoring
of errors for path prefixes and only improves the handling of the unusual ambiguous error
EFAULT and the unusual error EIO. The behaviour was changed to match the behaviour of
The execl(), execle(), execlp(), execvp() and execvP() functions may fail and set errno for
any of the errors specified for the library functions execve(2) and malloc(3).
The exect() and execv() functions may fail and set errno for any of the errors specified for
the library function execve(2).
sh(1), execve(2), fork(2), ktrace(2), ptrace(2), environ(7)
The execl(), execv(), execle(), execlp() and execvp() functions conform to IEEE Std
1003.1-1988 (``POSIX.1''). The execvP() function first appeared in FreeBSD 5.2.
BSD January 24, 1994 BSD