diff --git a/sys/unix/Makefile.doc b/sys/unix/Makefile.doc
index 5dbe117f0..044632a2d 100644
--- a/sys/unix/Makefile.doc
+++ b/sys/unix/Makefile.doc
@@ -9,15 +9,24 @@ NHSROOT=..
 # for Atari
 # SHELL=E:/GEMINI2/MUPFEL.TTP
 
-MAKEDEFS = ../util/makedefs
+MAKEDEFS ?= ../util/makedefs
+# Only generate output for the current configuration:
+NHGREP ?= $(MAKEDEFS) --grep --input - --output -
+NEEDMAKEDEFS ?= $(MAKEDEFS)
+# Generate output for all configurations:
+#NHGREP ?= $(MAKEDEFS) --grep --input - --output - --grep-define ALLDOCS
+#NEEDMAKEDEFS ?= $(MAKEDEFS)
+# Fallback:
+#NHGREP ?= cat
+#NEEDMAKEDEFS ?=
 
-#STRIPBS ?= ../util/stripbs
 NROFF ?= nroff
+# NROFF_FLAGS comes from a hints file, or is empty
 
 # Which version do we want to build?  (XXX These are not used anywhere.)
-GUIDEBOOK = Guidebook		# regular ASCII file
-#GUIDEBOOK = Guidebook.ps	# PostScript file
-#GUIDEBOOK = Guidebook.dvi	# TeX device-independent file
+GUIDEBOOK ?= Guidebook		# regular ASCII file
+#GUIDEBOOK ?= Guidebook.ps	# PostScript file
+#GUIDEBOOK ?= Guidebook.dvi	# TeX device-independent file
 
 # Some versions of col need -x to keep them from converting spaces to tabs;
 # some versions of col don't do the conversion by default and don't
@@ -29,39 +38,33 @@ COLCMD ?= col -bx
 #COLCMD ?= $(STRIPBS)
 
 # The command to use to generate a PostScript file
-# PSCMD = ditroff | psdit
+# PSCMD ?= ditroff | psdit
 PSCMD ?= groff
 
-# Use the "cat" GUIDECMD if nroff and/or tbl and/or col are not installed
-# Not appropriate for creating Guidebook.txt.
-# GUIDECMD ?= cat Guidebook.txt
-#
-# Single page. Might need adjustment to .pl value
-# GUIDECMD= $(GUIDE_PREFORMAT) | perl -pe 's/^(.mt)$$/.pl 4720v\n.in 0\n.po 8\n.ll 64m\n$$1/' | $(NROFF) -c -Tascii | $(COLCMD)
-#
-GUIDECMD ?= $(GUIDE_PREFORMAT) | $(NROFF) -c -Tascii $(NROFF_FLAGS) | $(COLCMD)
-ONEPAGECMD ?= $(ONEPAGE_PREFORMAT) | $(NROFF) -c -Tascii $(NROFF_FLAGS) | $(COLCMD)
-
-# Only generate output for the current configuration:
-NHGREP = $(MAKEDEFS) --grep --input - --output -
-NEEDMAKEDEFS = $(MAKEDEFS)
-# Generate output for all configurations:
-#NHGREP = $(MAKEDEFS) --grep --input - --output - --grep-define ALLDOCS
-#NEEDMAKEDEFS = $(MAKEDEFS)
-# Fallback:
-#NHGREP = cat
-#NEEDMAKEDEFS =
-
 GUIDEBOOK_MN_SRC ?= Guidebook.mn
 GUIDEBOOK_MN ?= $(GUIDEBOOK_MN_SRC)
-GUIDEBOOK_TEX_SRC ?= Guidebook.tex
-GUIDEBOOK_TEX ?= $(GUIDEBOOK_TEX_SRC)
 
 GUIDE_PREFORMAT ?= cat $(GUIDEBOOK_MN) | $(NHGREP) | tbl tmac.n -
 # for Guidebook.dat, unpaginated version of Guidebook.txt
 ONEPAGE_PREFORMAT ?= cat Gbk-1pg-pfx.mn $(GUIDEBOOK_MN) Gbk-1pg-sfx.mn \
 	| $(NHGREP) | tbl tmac.n -
+ONEPAGECMD ?= $(ONEPAGE_PREFORMAT) | nroff -c -Tascii $(NROFF_FLAGS) | $(COLCMD)
+# Use the "cat" GUIDECMD if nroff and/or tbl and/or col are not installed
+# Not appropriate for creating Guidebook.txt.
+# GUIDECMD ?= cat Guidebook.txt
+#
+# Single page. Might need adjustment to .pl value
+# GUIDECMD ?= $(GUIDE_PREFORMAT) | perl -pe 's/^(.mt)$$/.pl 4720v\n.in 0\n.po 8\n.ll 64m\n$$1/' | nroff -c -Tascii | $(COLCMD)
+#
+GUIDECMD ?= $(GUIDE_PREFORMAT) | nroff -c -Tascii $(NROFF_FLAGS) | $(COLCMD)
+GUIDEBOOK_TEX_SRC ?= Guidebook.tex
+GUIDEBOOK_TEX ?= $(GUIDEBOOK_TEX_SRC)
 
+#STRIPBS ?= ../util/stripbs
+# STRIPBS often comes from a hints file, or is empty
+
+# targets
+#
 # the basic guidebook
 Guidebook	: $(GUIDEBOOK_MN) tmac.n tmac.nh $(NEEDMAKEDEFS) $(STRIPBS)
 	-$(GUIDECMD) > Guidebook
@@ -99,10 +102,10 @@ RCVRMANCREATE = cat recover.6 | $(NHGREP) >
 DLBMANCREATE = cat dlb.6 | $(NHGREP) >
 MDMANCREATE = cat makedefs.6 | $(NHGREP) >
 # manual installation for most SYSV-style systems
-# GAMEMANCREATE = cat nethack.6 | $(NHGREP) | $(NROFF) -man - >
-# RCVRMANCREATE = cat recover.6 | $(NHGREP) | $(NROFF) -man - >
-# DLBMANCREATE = cat dlb.6 | $(NHGREP) | $(NROFF) -man - >
-# MDMANCREATE = cat makedefs.6 | $(NHGREP) | $(NROFF) -man - >
+# GAMEMANCREATE = cat nethack.6 | $(NHGREP) | nroff -man - >
+# RCVRMANCREATE = cat recover.6 | $(NHGREP) | nroff -man - >
+# DLBMANCREATE = cat dlb.6 | $(NHGREP) | nroff -man - >
+# MDMANCREATE = cat makedefs.6 | $(NHGREP) | nroff -man - >
 
 manpages: $(PREMANPAGES)
 	-$(GAMEMANCREATE) $(MANDIR)/$(GAME).$(MANEXT)