EXECL(3)                       Library Routines                       EXECL(3)

NAME

       execl, execlp, execv, execvp - execute a file

SYNOPSIS

       #include <unistd.h>

       extern char **environ;

       int execl(const char *path, const char *arg, ...);
       int execle(const char *path, const char *rg, ...);
       int execlp(const char *file, const char *arg, ...);
       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  arg and subsequent ellipses in the execl, execle, and execlp func‐
       tions can be thought of as arg0, arg1, ..., argn.   Together  they  de‐
       scribe  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  execle  function  expects  a final argument, envp, of type 'char *
       const *' to follow the trailing NULL pointer.  This is an array of  en‐
       vironment  strings, similar to that used by execve(2).  This array must
       be NULL-terminated.

       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 begin executed.  The array of point‐
       ers must be terminated by a NULL pointer.

       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 or a colon (:).  The search path  is  the
       path  specified  in the environment by PATH variable.  If this variable
       isn't specified, the default path /bin /usr/bin (or /usr/bin  /bin  for
       gsh(1)) is used.

RETURN VALUES

       If any of the exec functions returns, an error will have occurred.  The
       return value is SYSERR (-1), and the global variable errno will be  set
       to indicate the error.

ERRORS

       These  routines  may fail and set errno for any of the errors specified
       for the library functions execve(2), _execve(2), and malloc(3).

GNO IMPLEMENTATION

       When parsing the PATH environment variable, execvp  and  execlp  assume
       that  if  there is no colon (:) within PATH then the pathname delimiter
       is a slash (/).  This is to facilitate use  of  GS/OS  pathname  delim‐
       iters.

       The  current version of the gsh shell searches PATH from back to front.
       In most other shells, it is done front to back.  In  order  to  provide
       consistency  with  gsh,  PATH is currently scanned back to front.  With
       this backwards scanning, the default PATH used is  /usr/bin  /bin.   If
       gsh gets fixed, the scan order will be quickly changed.

AUTHOR

       Implemented from the BSD specification by Devin Reade.

SEE ALSO

       execve(2), fork(2), exec(3).

HISTORY

       The GNO implementation of these routines first appeared in the lenviron
       library.  They became part of the GNO distribution as of v2.0.6



GNO                             19 January 1997                       EXECL(3)