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nn. Library extensions
.PP
Some extensions have been made to the fortran library
corresponding to the system calls fork, exec, wait, sleep, signal
and kill.
See the Unix Programmers Manual for more details.
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call fork( npid )
	In the child, 'npid' is zero.
	In the parent, it is the pid of the child,
	or -1 if the fork failed.

call exec( name, args,... )
	The file 'name' is executed with the given arguments.
	By convention, the first program argument is the
	name of the program called.
	The arguments do not terminate with a zero, as distinct
	from "C" and assembler.

	Note that the call does NOT return, unless the program
	could not be found, or some other error was found.

call wait( nstat, npid )
	The process will wait for a child to terminate, in
	which case the pid & status are returned.

call sys (name, args ... )
	This corresponds to the 'EXEC' call, except that it
	is more like a subroutine call, since the routine
	performs a fork/exec/wait sequence internally.

	This call DOES return, unlike EXEC.

n = nsys( prog, args ... )
	Exactly like SYS, except it is a function call,
	and a value is returned viz
		0: ok
		-1: error.

call sleep( nsecs )
	Go to sleep for "nsecs" seconds.

call signal( nsig, label, nold )
	Take action on signals received.
	nsig: the signal to process.
	label:		0: default action;
			1: ignore;
			otherwise assumed to be name of a
			subroutine to be called.
	nold: the old value of "label".

call kill( npid, isig, ierr )
	Send the signal "isig" to process "pid".
	If successful, ierr = 0, else it it -1.
