SYNOPSIS

     #include <unistd.h>

     extern char **environ;

     int
     execl(const char *path, const char *arg, ... /*, (char *)0 */);

     int
     execlp(const char *file, const char *arg, ... /*, (char *)0 */);

     int
     execle(const char *path, const char *arg, ...
         /*, (char *)0, char *const envp[] */);

     int
     execv(const char *path, char *const argv[]);

     int
     execvp(const char *file, char *const argv[]);

     int
     execvP(const char *file, const char *search_path, 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(2) 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(), execvp(), and execvP() functions provide an array of point-
     ers 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 specify the environment of the executed
     process by following the NULL pointer that terminates the list of argu-
     ments in the argument list or the pointer to the argv array with an addi-
     argument to the function.  In addition, certain errors are treated spe-
     cially.

     If an error is ambiguous (for simplicity, we shall consider all errors
     except ENOEXEC as being ambiguous here, although only the critical error
     EACCES is really ambiguous), then these functions will act as if they
     stat the file to determine whether the file exists and has suitable exe-
     cute permissions.  If it does, they will return immediately with the
     global variable errno restored to the value set by execve().  Otherwise,
     the search will be continued.  If the search completes without performing
     a successful execve() or terminating due to an error, these functions
     will return with the global variable errno set to EACCES or ENOENT
     according to whether at least one file with suitable execute permissions
     was found.

     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 VALUES

     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  The shell.

ERRORS

     The execl(), execle(), execlp(), execvp() and execvP() functions may fail
     and set errno for any of the errors specified for the library functions
     execve(2) and malloc(3).

     The execv() function may fail and set errno for any of the errors speci-
     fied for the library function execve(2).

SEE ALSO

     sh(1), execve(2), fork(2), ktrace(2), ptrace(2), environ(7)

COMPATIBILITY

     Historically, the default path for the execlp() and execvp() functions
     was ``:/bin:/usr/bin''.  This was changed to place the current directory
     last to enhance system security.

     The behavior of execlp() and execvp() when errors occur while attempting
     to execute the file is not quite historic practice, and has not tradi-
     tionally been documented and is not specified by the POSIX standard.

     Traditionally, the functions execlp() and execvp() ignored all errors
     except for the ones described above and ETXTBSY, upon which they retried
     after sleeping for several seconds, and ENOMEM and E2BIG, upon which they
     returned.  They now return for ETXTBSY, and determine existence and exe-

BSD                            January 24, 1994                            BSD