; Plot a heart with gnuplot:
plot [-2:2] acos(1-abs(x))-pi,sqrt(1-(abs(x)-1)^2)

; If readline is enabled,
; hitting the up arrow, then the Enter key, should allow a replot.
:push plot [-2:2] acos(1-abs(x))-pi,sqrt(1-(abs(x)-1)^2)