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

NAME
       execl, execlp, execle, execv, execvp, execvpe - 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[]);
       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
       front-ends  for execve(2).  (See	the manual page	for execve(2) for fur-
       ther 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  const  char	*arg and subsequent ellipses in	the execl(), execlp(),
       and execle() functions can be thought of	as arg0, arg1, ..., argn.  To-
       gether  they describe a list of one or more pointers to null-terminated
       strings that represent the argument list	available to the executed pro-
       gram.   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(), execvp(), and execvpe()  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() and	execvpe() functions allow the caller  to  specify  the
       environment  of	the  executed program via the argument envp.  The envp
       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
       calling process.

   Special semantics for execlp() and execvp()
       The  execlp(),  execvp(), and execvpe() functions duplicate the actions
       of the shell in searching for an	executable file	if the specified file-
       name does not contain a slash (/) character.  The file is sought	in the
       colon-separated list of directory pathnames specified in	the PATH envi-
       ronment	variable.   If	this variable isn't defined, the path list de-
       faults to the current directory followed	by the list of directories re-
       turned  by  confstr(_CS_PATH).  (This confstr(3)	call typically returns
       the value "/bin:/usr/bin".)

       If the specified	filename includes a slash character, then PATH is  ig-
       nored, 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.)

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).

VERSIONS
       The execvpe() function first appeared in	glibc 2.11.

CONFORMING TO
       POSIX.1-2001, POSIX.1-2008.

       The execvpe() function is a GNU extension.

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  attempt-
       ing 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  de-
       scribed above occurs.

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

COLOPHON
       This  page  is  part of release 3.74 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
       http://www.kernel.org/doc/man-pages/.

GNU				  2010-09-25			       EXEC(3)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

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