gs
  -o scaled.eps
  -sDEVICE=eps2write
  -c "<</Install {0.5 0.5 scale}>> setpagedevice"
  -f input.eps

gs -q -o -sDEVICE=bbox input.eps
  %%BoundingBox: 41 19 585 831
  %%HiResBoundingBox: 41.990975 19.997999 584.027982 830.009014

gs -q -o -sDEVICE=bbox scaled.eps
  %%BoundingBox: 20 9 293 416
  %%HiResBoundingBox: 20.991023 9.990000 292.013991 415.008972

gs
  -o A4-landscape.eps
  -sDEVICE=eps2write
  -c "<</Install {1.4151 0.7066 scale}>> setpagedevice"
  -f A4-portrait.eps

sudo port -pf install ghostscript