refrain from forcing a hardwired SHELL value, cf. 1494ded298a6 but it becomes obsolete again in 549969a7f582 and follow-ups;
#!/usr/bin/env bash
#
# psbooklet - rearrange pages of ps file to be printed as booklet (duplex)
psbook "$@" | \
pstops '4:0L@.7(21cm,0cm)+1L@.7(21cm,14.85cm),3R@.7(0cm,14.85cm)+2R@.7(0cm,29.7cm)'