  Semi-inclusive deep inelastic scattering on nuclear targets is an ideal tool
to study the energy loss effect of an outgoing quark in a nuclear medium. By
means of the short hadron formation time, the experimental data with quark
hadronization occurring outside the nucleus are picked out. A leading-order
analysis is performed for the hadron multiplicity ratios as a function of the
energy fraction on helium, neon, and copper nuclei relative to deuteron for the
various identified hadrons. It is shown that the nuclear effects on parton
distribution functions can be neglected. It is found that the theoretical
results considering the nuclear modification of fragmentation functions due to
quark energy loss are in good agreement with the experimental data. Whether the
quark energy loss is linear or quadratic with the path length is not
determined. The obtained energy loss per unit length is 0.38 \pm 0.03 GeV/fm
for an outgoing quark by the global fit.
