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 associated 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
       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  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
       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.)

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
       indicate 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 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.

CONFORMING TO

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

BSD MANPAGE
							    1993-11-29								   EXEC(3)