It’s easy using pdftops, part of the Poppler suite of programs. First make sure it’s installed, or install it (using Homebrew on OS X):

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$ brew update
$ brew install poppler

Then the command pdftops infile.pdf outfile.ps can be scripted as per usual, something like this:

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for page in pages/*.pdf
do
  pdftops $page postscript/`basename -s .pdf $page`.ps
done

Recorded in the interest of helping Google organise my brain.