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execl(3)							      execl(3)

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

       execl(name, arg0, arg1, ..., argn, (char *)0)
       char *name, *arg0, *arg1, ..., *argn;

       execv(name, argv)
       char *name, *argv[];

       execle(name, arg0, arg1, ..., argn, (char *)0, envp)
       char *name, *arg0, *arg1, ..., *argn, *envp[];

       execlp(file, arg0, arg1, ..., argn, (char *)0)
       char *file, *arg0, *arg1, ..., *argn;

       char *file, *argv[];

       exect(name, argv, envp)
       char *name, *argv[], *envp[];

       extern char **environ;

       These routines provide various interfaces to the system call.  Refer to
       for a description of their properties; only brief descriptions are pro‐
       vided here.

       In  all	their  forms, these calls overlay the calling process with the
       named file, then transfer to the entry point of the core image  of  the
       file.  There can be no return from a successful exec.  The calling core
       image is lost.

       The name argument is a pointer to the name of the file to be  executed.
       The pointers arg[0], arg[1] ...	address null-terminated strings.  Con‐
       ventionally arg[0] is the name of the file.

       Two interfaces are available.  is useful when a known file  with	 known
       arguments  is  being called; the arguments to are the character strings
       constituting the file and the arguments; the first argument is  conven‐
       tionally	 the same as the file name (or its last component).  A 0 argu‐
       ment must end the argument list.

       The version is useful when  the	number	of  arguments  is  unknown  in
       advance.	  The arguments to are the name of the file to be executed and
       a vector of strings containing the arguments.  The last argument string
       must be followed by a 0 pointer.

       The  version  is	 used when the executed file is to be manipulated with
       The program is forced to single step a single  instruction  giving  the
       parent  an  opportunity to manipulate its state.	 On the VAX-11 this is
       done by setting the trace bit in the process status longword.

       When a C program is executed, it is called as follows:
	    main(argc, argv, envp)
	    int argc;
	    char **argv, **envp;
       where argc is the argument count and argv  is  an  array	 of  character
       pointers	 to  the  arguments themselves.	 As indicated, argc is conven‐
       tionally at least one and the first member of the  array	 points	 to  a
       string containing the name of the file.

       The argv is directly usable in another because argv[argc] is 0.

       The  envp is a pointer to an array of strings that constitute the envi‐
       ronment of the process.	Each string consists of a name, an “=”, and  a
       null-terminated	value.	 The array of pointers is terminated by a null
       pointer.	 The shell passes an environment entry for each	 global	 shell
       variable	 defined when the program is called.  See for some convention‐
       ally used names.	 The C run-time start-off routine  places  a  copy  of
       envp in the global cell which is used by and to pass the environment to
       any subprograms executed by the current program.

       The and routines are called with the same arguments as and  but	dupli‐
       cate  the shell's actions in searching for an executable file in a list
       of directories.	The directory list is obtained from the environment.

       If is called to execute a file that turns out to	 be  a	shell  command
       file,  and  if  it  is  impossible  to execute the shell, the values of
       argv[0] and argv[-1] will be modified before return.

       The function receives a SIGILL error if passed a PATH  list  that  con‐
       tains names greater than NAME_MAX (255) characters long.

       If  the	file  cannot be found, if it is not executable, if it does not
       start with a valid magic number, if maximum memory is exceeded,	or  if
       the arguments require too much space, a return constitutes the diagnos‐
       tic; the return value is -1.  For further information, see Even for the
       super-user, at least one of the execute-permission bits must be set for
       a file to be executed.

       Shell, invoked if command file found
			   by or

See Also
       csh(1), execve(2), fork(2), environ(7)

				      VAX			      execl(3)

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