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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 the function execve(2).  (See the	manual page for	execve
       for detailed information	about the replacement of the current process.)

       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 file name	 asso-
       ciated  with  the  file	being executed.	 The list of arguments must be
       terminated by a NULL pointer.

       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
       file name associated with the file being	executed.  The array of	point-
       ers 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 argu-
       ments in	the parameter list or the pointer to the argv  array  with  an
       additional  parameter.  This additional parameter is an array of	point-
       ers 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 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.  The search path is the  path  specified
       in the environment by the PATH variable.	 If this variable isn't	speci-
       fied, the default path ``:/bin:/usr/bin'' is used.  In  addition,  cer-
       tain errors are treated specially.

       If  permission is denied	for a file (the	attempted execve returned EAC-
       CES), these functions will continue searching the rest  of  the	search
       path.   If  no  other file is found, however, they will return with the
       global variable errno set to EACCES.

       If the header of	a file isn't 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 search-
       ing is done.)

RETURN VALUE
       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	 indi-
       cate the	error.

FILES
       /bin/sh

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

SEE ALSO
       sh(1), execve(2), fork(2), environ(5), ptrace(2)

COMPATIBILITY
       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  traditionally  been
       documented  and is not specified	by the POSIX standard. BSD (and	possi-
       bly other systems) do an	automatic sleep	and retry if  ETXTBSY  is  en-
       countered. Linux	treats it as a hard error and returns immediately.

       Traditionally,  the  functions execlp and execvp	ignored	all errors ex-
       cept 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.

CONFORMING TO
       execl, execv, execle, execlp and	execvp conform	to  IEEE  Std1003.1-88
       (``POSIX.1'').

BSD MANPAGE			  1993-11-29			       EXEC(3)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | FILES | ERRORS | SEE ALSO | COMPATIBILITY | CONFORMING TO

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