chkopen
renamef(chkopen(devnull, 0), 0);
input = chkopen(cmdadr, 0);
input = chkopen(p, 0);
subst(chkopen(ion, 0), (fd = tmpfil(&tb)));
fd = chkopen(tmpout, 0);
fd = chkopen(ion, 0);
fd = chkopen(ion, newmode);