  We consider a 0-$\pi$ Josephson junction consisting of asymmetric 0 and $\pi$
regions of different lengths $L_0$ and $L_\pi$ having different critical
current densities $j_{c,0}$ and $j_{c,\pi}$. If both segments are rather short,
the whole junction can be described by an \emph{effective} current-phase
relation for the spatially averaged phase $\psi$, which includes the usual term
$\propto\sin(\psi)$, a \emph{negative} second harmonic term
$\propto\sin(2\psi)$ as well as the unusual term $\propto H \cos\psi$ tunable
by magnetic field $H$. Thus one obtains an electronically tunable current-phase
relation. At H=0 this corresponds to the $\varphi$ Josephson junction.
