#include <stdio.h>#include <signal.h>#define	tst(a,b)	(*mode == 'r'? (b) : (a))#define	RDR	0#define	WTR	1static	int	popen_pid[20];FILE *popen(cmd,mode)char	*cmd;char	*mode;{	int p[2];	register myside, hisside, pid;	if(pipe(p) < 0)		return NULL;	myside = tst(p[WTR], p[RDR]);	hisside = tst(p[RDR], p[WTR]);	if((pid = fork()) == 0) {		/* myside and hisside reverse roles in child */		close(myside);		dup2(hisside, tst(0, 1));		close(hisside);		execl("/bin/sh", "sh", "-c", cmd, 0);		_exit(1);	}	if(pid == -1)		return NULL;	popen_pid[myside] = pid;	close(hisside);	return(fdopen(myside, mode));}pclose(ptr)FILE *ptr;{	register f, r, (*hstat)(), (*istat)(), (*qstat)();	int status;	f = fileno(ptr);	fclose(ptr);	istat = signal(SIGINT, SIG_IGN);	qstat = signal(SIGQUIT, SIG_IGN);	hstat = signal(SIGHUP, SIG_IGN);	while((r = wait(&status)) != popen_pid[f] && r != -1)		;	if(r == -1)		status = -1;	signal(SIGINT, istat);	signal(SIGQUIT, qstat);	signal(SIGHUP, hstat);	return(status);}