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

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

       #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[]);

       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 cur-
       rent process.)

       The initial argument for these functions is the pathname of a file which  is  to  be  exe-

       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  associ-
       ated  with  the	file  being executed.  The list of arguments must be terminated by a 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 file name 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  parameter  list  or  the
       pointer	to  the argv array with an additional parameter.  This additional parameter 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 vari-
       able 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  vari-
       able  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 returned EACCES), 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 searching is done.)

       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.


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

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

       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 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.

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

BSD MANPAGE				    1993-11-29					  EXEC(3)
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