EXEC(3) 						     Linux Programmer's Manual							   EXEC(3)

NAME

       execl, execlp, execle, execv, execvp - execute a file

SYNOPSIS

       #include <unistd.h>

       extern char **environ;

       int execl(const char *path, const char *arg, ...);
       int execlp(const char *file, const char *arg, ...);
       int execle(const char *path, const char *arg,
		  ..., char * const envp[]);
       int execv(const char *path, char *const argv[]);
       int execvp(const char *file, char *const argv[]);

DESCRIPTION

       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 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 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.

       The  execv()  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 filename associated with the file being executed.   The  array	of
       pointers must be terminated by a NULL pointer.

       The  execle()  function	also  specifies  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.

   Special semantics for execlp() and execvp()
       The functions execlp() and execvp() will duplicate the actions of the shell in searching for an executable file if the  specified  filename
       does  not  contain a slash (/) character.  The search path is the path specified in the environment by the PATH variable.  If this variable
       isn't specified, the default path ":/bin:/usr/bin" is used.  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.)

RETURN VALUE

       If any of the exec() functions returns, an error will have occurred.  The return value is -1, and errno will be set to indicate the error.

ERRORS

       All of these functions may fail and set errno for any of the errors specified for the library function execve(2).

CONFORMING TO

       POSIX.1-2001.

NOTES

       On some other systems the default path (used when the environment does not contain the variable PATH) has  the  current	working  directory
       listed after /bin and /usr/bin, as an anti-Trojan-horse measure.  Linux uses here the traditional "current directory first" default path.

       The  behavior  of execlp() and execvp() when errors occur while attempting to execute the file is historic practice, but has not tradition-
       ally 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.

SEE ALSO

       sh(1), execve(2), fork(2), ptrace(2), fexecve(3), environ(7)

COLOPHON

       This page is part of release 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

GNU
								    2009-02-22								   EXEC(3)