execl (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
       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 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 pro-
       cess 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 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.




       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  possi-
       bly  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

BSD MANPAGE                       1993-11-29                           exec(3)