diff --git a/scripts/mc.sh b/scripts/mc.sh
index 306ea07ea..b56846977 100644
--- a/scripts/mc.sh
+++ b/scripts/mc.sh
@@ -12,9 +12,9 @@
 # Environment variables: MERCURY_INT_DIR, MERCURY_DEP_DIR, MERCURY_C_INCL_DIR,
 # MERCURY_COMPILER.
 
-INTDIR=${MERCURY_INT_DIR:-@LIBDIR@/ints}
-DEPDIR=${MERCURY_DEP_DIR:-@LIBDIR@/deps}
-C_INCL=${MERCURY_C_INCL_DIR:-@LIBDIR@/inc}
-MC=${MERCURY_COMPILER:-"@LIBDIR@/bin/@FULLARCH@/mercury_compile"}
+INTDIR=${MERCURY_INT_DIR=@LIBDIR@/ints}
+DEPDIR=${MERCURY_DEP_DIR=@LIBDIR@/deps}
+C_INCL=${MERCURY_C_INCL_DIR=@LIBDIR@/inc}
+MC=${MERCURY_COMPILER="@LIBDIR@/bin/@FULLARCH@/mercury_compile"}
 
 exec $MC -- -I "$INTDIR" -I "$DEPDIR" --c-include-directory "$C_INCL" "$@"
diff --git a/scripts/mcn.sh b/scripts/mcn.sh
index 5c629d75a..69a340b1a 100644
--- a/scripts/mcn.sh
+++ b/scripts/mcn.sh
@@ -12,9 +12,9 @@
 # Environment variables: MERCURY_INT_DIR, MERCURY_DEP_DIR, MERCURY_C_INCL_DIR,
 # MERCURY_COMPILER.
 
-INTDIR=${MERCURY_INT_DIR:-@LIBDIR@/ints}
-DEPDIR=${MERCURY_DEP_DIR:-@LIBDIR@/deps}
-C_INCL=${MERCURY_C_INCL_DIR:-@LIBDIR@/inc}
-MC=${MERCURY_COMPILER:-@LIBDIR@/nuprolog/@FULLARCH@/mercury_compile.nu}
+INTDIR=${MERCURY_INT_DIR=@LIBDIR@/ints}
+DEPDIR=${MERCURY_DEP_DIR=@LIBDIR@/deps}
+C_INCL=${MERCURY_C_INCL_DIR=@LIBDIR@/inc}
+MC=${MERCURY_COMPILER=@LIBDIR@/nuprolog/@FULLARCH@/mercury_compile.nu}
 
 exec $MC -I "$INTDIR" -I "$DEPDIR" --c-include-directory "$C_INCL" "$@"
diff --git a/scripts/mcs.sh b/scripts/mcs.sh
index cb80409ff..823964395 100644
--- a/scripts/mcs.sh
+++ b/scripts/mcs.sh
@@ -12,9 +12,9 @@
 # Environment variables: MERCURY_INT_DIR, MERCURY_DEP_DIR, MERCURY_C_INCL_DIR,
 # MERCURY_COMPILER_SICSTUS.
 
-INTDIR=${MERCURY_INT_DIR:-@LIBDIR@/ints}
-DEPDIR=${MERCURY_DEP_DIR:-@LIBDIR@/deps}
-C_INCL=${MERCURY_C_INCL_DIR:-@LIBDIR@/inc}
-MCS=${MERCURY_COMPILER_SICSTUS:-@LIBDIR@/sicstus/@FULLARCH@/mercury_compile.sicstus}
+INTDIR=${MERCURY_INT_DIR=@LIBDIR@/ints}
+DEPDIR=${MERCURY_DEP_DIR=@LIBDIR@/deps}
+C_INCL=${MERCURY_C_INCL_DIR=@LIBDIR@/inc}
+MCS=${MERCURY_COMPILER_SICSTUS=@LIBDIR@/sicstus/@FULLARCH@/mercury_compile.sicstus}
 
 exec $MCS -I "$INTDIR" -I "$DEPDIR" --c-include-directory "$C_INCL" "$@"
diff --git a/scripts/mgnuc.sh b/scripts/mgnuc.sh
index 70f7ce13a..72f8bf892 100644
--- a/scripts/mgnuc.sh
+++ b/scripts/mgnuc.sh
@@ -30,7 +30,7 @@
 # -Wenum-clash 		is for C++ only
 # -Wunused		causes various spurious warnings
 
-C_INCL_DIR=${MERCURY_C_INCL_DIR:-@LIBDIR@/inc}
+C_INCL_DIR=${MERCURY_C_INCL_DIR=@LIBDIR@/inc}
 
 CHECK_OPTS="-ansi
       -Wall -Wwrite-strings -Wpointer-arith -Wcast-qual -Wtraditional -Wshadow
diff --git a/scripts/mint.sh b/scripts/mint.sh
index 3010096e6..387477218 100644
--- a/scripts/mint.sh
+++ b/scripts/mint.sh
@@ -9,7 +9,7 @@
 #
 # Usage: mint module-name ...
 
-INTDIR=${MERCURY_INT_DIR:-@LIBDIR@/ints}
+INTDIR=${MERCURY_INT_DIR=@LIBDIR@/ints}
 
 exit_status=0
 
@@ -23,7 +23,7 @@ for arg in "$@"; do
 	module="`basename $arg .nl`"
 	file="$INTDIR/$module.int"
 	if [ -r "$file" ]; then
-		${PAGER:-more} "$file"
+		${PAGER=more} "$file"
 	else
 		echo "`basename $0`: no interface file for \`$module'." 1>&2
 		exit_status=1
diff --git a/scripts/ml.sh b/scripts/ml.sh
index a1e94f9ef..c71dd3f75 100644
--- a/scripts/ml.sh
+++ b/scripts/ml.sh
@@ -19,7 +19,7 @@
 #
 # Environment variables: MERCURY_C_LIB_DIR
 
-LIBDIR=${MERCURY_C_LIB_DIR:-@LIBDIR@/lib}
+LIBDIR=${MERCURY_C_LIB_DIR=@LIBDIR@/lib}
 verbose=false
 GRADE=asm_fast.gc
 
@@ -81,7 +81,7 @@ case "`hostname`" in
 	kryten.cs.mu.OZ.AU)
 		GCC=/usr/local/bin/gcc ;;
 	*)
-		GCC=${GCC:-gcc}
+		GCC=${GCC=gcc}
 esac
 
 if $verbose; then
diff --git a/scripts/mmake.sh b/scripts/mmake.sh
index 94a97eefe..556fa98e2 100644
--- a/scripts/mmake.sh
+++ b/scripts/mmake.sh
@@ -11,10 +11,10 @@
 #
 #-----------------------------------------------------------------------------#
 
-MAKE=${MMAKE_MAKE:-make}
-MMAKE_VARS=${MMAKE_VARS:-@LIBDIR@/mmake/Mmake.vars}
-MMAKE_RULES=${MMAKE_RULES:-@LIBDIR@/mmake/Mmake.rules}
-MERCURY_INT_DIR=${MERCURY_INT_DIR:-@LIBDIR@/ints}
+MAKE=${MMAKE_MAKE=make}
+MMAKE_VARS=${MMAKE_VARS=@LIBDIR@/mmake/Mmake.vars}
+MMAKE_RULES=${MMAKE_RULES=@LIBDIR@/mmake/Mmake.rules}
+MERCURY_INT_DIR=${MERCURY_INT_DIR=@LIBDIR@/ints}
 
 MMAKE=$0
 verbose=false
diff --git a/scripts/mnc.sh b/scripts/mnc.sh
index 160062537..f6e58b592 100644
--- a/scripts/mnc.sh
+++ b/scripts/mnc.sh
@@ -13,7 +13,7 @@
 #
 # Environment variables: MERCURY_NC_BUILTIN
 
-nc_builtin_nl=${MERCURY_NC_BUILTIN:-@LIBDIR@/nuprolog/nc_builtin.nl}
+nc_builtin_nl=${MERCURY_NC_BUILTIN=@LIBDIR@/nuprolog/nc_builtin.nl}
 
 options=
 
@@ -58,5 +58,5 @@ for file in "$@"; do
 	fi
 	nc -c $options $tmp.nl
 	rm $tmp.nl $tmp.ns
-	mv $tmp.no ${target:-"$rootname.no"}
+	mv $tmp.no ${target="$rootname.no"}
 done
diff --git a/scripts/mnl.sh b/scripts/mnl.sh
index ce261149d..c529060e5 100644
--- a/scripts/mnl.sh
+++ b/scripts/mnl.sh
@@ -14,8 +14,8 @@
 #
 # Environment variables: MERCURY_LIB_DIR, MERCURY_LIB_OBJS
 
-NULIBDIR=${MERCURY_LIB_DIR:-@LIBDIR@/nuprolog/@FULLARCH@}
-LIBRARY_OBJS=${MERCURY_LIB_OBJS:-`cd $NULIBDIR; echo *.no`}
+NULIBDIR=${MERCURY_LIB_DIR=@LIBDIR@/nuprolog/@FULLARCH@}
+LIBRARY_OBJS=${MERCURY_LIB_OBJS=`cd $NULIBDIR; echo *.no`}
 
 options=
 verbose=false
diff --git a/scripts/mnp.sh b/scripts/mnp.sh
index e73ffcc4e..484a211d1 100644
--- a/scripts/mnp.sh
+++ b/scripts/mnp.sh
@@ -13,6 +13,6 @@
 #
 # Environment variables: MERCURY_INTERPRETER
 
-INTERPRETER=${MERCURY_INTERPRETER:-@LIBDIR@/nuprolog/@FULLARCH@/library.nu}
+INTERPRETER=${MERCURY_INTERPRETER=@LIBDIR@/nuprolog/@FULLARCH@/library.nu}
 
 exec $INTERPRETER "$@"
diff --git a/scripts/mod2init.sh b/scripts/mod2init.sh
index 99e5a82ad..8805da4c6 100644
--- a/scripts/mod2init.sh
+++ b/scripts/mod2init.sh
@@ -13,8 +13,8 @@
 #
 # Environment variables: MERCURY_MOD_LIB_DIR, MERCURY_MOD_LIB_MODS.
 
-MERCURY_MOD_LIB_DIR=${MERCURY_MOD_LIB_DIR:-@LIBDIR@/modules}
-MERCURY_MOD_LIB_MODS=${MERCURY_MOD_LIB_MODS:-@LIBDIR@/modules/*}
+MERCURY_MOD_LIB_DIR=${MERCURY_MOD_LIB_DIR=@LIBDIR@/modules}
+MERCURY_MOD_LIB_MODS=${MERCURY_MOD_LIB_MODS=@LIBDIR@/modules/*}
 
 # maximum number of calls to put in a single function
 calls_per_func=50
diff --git a/scripts/msc.sh b/scripts/msc.sh
index 4189e5410..eb43b5c54 100644
--- a/scripts/msc.sh
+++ b/scripts/msc.sh
@@ -11,9 +11,9 @@
 #
 # Use `msc -h' for help.
 
-sp_builtin_pl=${MERCURY_SP_BUILTIN:-@LIBDIR@/sicstus/sp_builtin.pl}
+sp_builtin_pl=${MERCURY_SP_BUILTIN=@LIBDIR@/sicstus/sp_builtin.pl}
 sicstus_compile=\
-${MERCURY_SICSTUS_COMPILER:-@LIBDIR@/sicstus/@FULLARCH@/sicstus_compile}
+${MERCURY_SICSTUS_COMPILER=@LIBDIR@/sicstus/@FULLARCH@/sicstus_compile}
 
 help=false
 compile_mode=fastcode
@@ -101,5 +101,5 @@ for file in "$@"; do
 	' $file > $tmp.pl
 	$sicstus_compile $compile_mode $tmp.pl
 	rm $tmp.pl 
-	mv $tmp.ql ${target:-"$rootname.ql"}
+	mv $tmp.ql ${target="$rootname.ql"}
 done
diff --git a/scripts/msl.sh b/scripts/msl.sh
index 811944a2f..937c21ff7 100644
--- a/scripts/msl.sh
+++ b/scripts/msl.sh
@@ -18,9 +18,9 @@
 #	-o, --output
 # Environment variables: MERCURY_SP_LIB_DIR, MERCURY_SP_LIB_OBJS
 
-SP=${MERCURY_SICSTUS_PROLOG:-@LIBDIR@/sicstus/@FULLARCH@/library.sicstus.debug}
-SPLIBDIR=${MERCURY_SP_LIB_DIR:-@LIBDIR@/sicstus/@FULLARCH@}
-LIBRARY_OBJS=${MERCURY_SP_LIB_OBJS:-`cd $SPLIBDIR; echo *.ql`}
+SP=${MERCURY_SICSTUS_PROLOG=@LIBDIR@/sicstus/@FULLARCH@/library.sicstus.debug}
+SPLIBDIR=${MERCURY_SP_LIB_DIR=@LIBDIR@/sicstus/@FULLARCH@}
+LIBRARY_OBJS=${MERCURY_SP_LIB_OBJS=`cd $SPLIBDIR; echo *.ql`}
 
 verbose=false
 debug=false
diff --git a/scripts/msp.sh b/scripts/msp.sh
index 37b77639e..398379734 100644
--- a/scripts/msp.sh
+++ b/scripts/msp.sh
@@ -14,6 +14,6 @@
 # Environment variables: MERCURY_SICSTUS_INTERPRETER
 
 INTERPRETER=\
-${MERCURY_SICSTUS_INTERPRETER:-@LIBDIR@/sicstus/@FULLARCH@/library.sicstus}
+${MERCURY_SICSTUS_INTERPRETER=@LIBDIR@/sicstus/@FULLARCH@/library.sicstus}
 
 exec $INTERPRETER "$@"