refactor configure script

Generate a makefile config instead of a makefile with predefined
constants. This makes the build a bit more easier to modify. Also
improve the makefile and apply some suggestions from shellcheck. :)

.gitignore

@@ -4,4 +4,4 @@
 esv
 result
 
-Makefile
+config.mk

Makefile

@@ -0,0 +1,29 @@
+IMPORT    = import
+PREFIX    = /usr/local
+MANPREFIX = ${PREFIX}/man
+
+DC      = ${_DC}
+CFLAGS  = ${_CFLAGS}
+OBJS    = ${_OBJS}
+
+all: esv
+
+include config.mk
+
+esv: ${OBJS}
+	${DC} ${_LDFLAGS} -of=$@ ${OBJS}
+
+.SUFFIXES: .d .o
+
+.d.o:
+	${DC} ${CFLAGS} -c $<
+
+clean:
+	rm -f esv ${OBJS} ${INIOBJS}
+
+install: esv
+	install -Dm755 esv ${DESTDIR}${PREFIX}/bin/esv
+	install -Dm644 esv.1 ${DESTDIR}${MANPREFIX}/man1
+	install -Dm644 esv.conf.5 ${DESTDIR}${MANPREFIX}/man5
+
+.PHONY: all clean install

configure

@@ -4,40 +4,9 @@
 
 set -e
 
-import=import
+mkf=config.mk
-
-mkf=Makefile
 objs='esv.o esvapi.o initial.o'
 srcs='esv.d esvapi.d initial.d'
-makefile='
-IMPORT    = '"$import"'
-PREFIX    = /usr/local
-MANPREFIX = ${PREFIX}/man
-
-DC      = ${_DC}
-CFLAGS  = ${_CFLAGS}
-OBJS    = ${_OBJS}
-
-all: esv
-
-esv: ${OBJS}
-	${DC} ${_LDFLAGS} -of=$@ ${OBJS}
-
-.SUFFIXES: .d .o
-
-.d.o:
-	${DC} ${CFLAGS} -c $<
-
-clean:
-	rm -f esv ${OBJS} ${INIOBJS}
-
-install:
-	install -Dm755 esv ${DESTDIR}${PREFIX}/bin/esv
-	install -Dm644 esv.1 ${DESTDIR}${MANPREFIX}/man1/esv.1
-	install -Dm644 esv.conf.5 ${DESTDIR}${MANPREFIX}/man5/esv.conf.5
-
-.PHONY: all clean install
-'
 
 # utility functions
 
@@ -45,10 +14,10 @@ present () {
 	command -v "$1" 1>/dev/null 2>/dev/null
 }
 using () {
-	>&2 printf "using $1\n"
+	>&2 printf "using %s\n" "$1"
 }
-error () {
+throw () {
-	>&2 printf "$(basename $0): $1\n"
+	>&2 printf "%s: %s\n" "$(basename "$0")" "$1"
 	exit 1
 }
 
@@ -56,7 +25,7 @@ error () {
 
 ## D compiler
 gen_DC () {
-	if ! [ -z "$dc" ]; then
+	if [ -n "$dc" ]; then
 		using "$dc"
 		return 0
 	fi
@@ -65,7 +34,7 @@ gen_DC () {
 	elif present dmd; then
 		dc=dmd
 	else
-		error "D compiler not found; install ldc or dmd"
+		throw "D compiler not found; install ldc or dmd"
 	fi
 
 	using "$dc"
@@ -101,7 +70,7 @@ gen_LDFLAGS () {
 		fi
 	fi
 	if [ -z "$debug" ]; then
-		if ! [ -z "$ldflags" ]; then ldflags="$ldflags "; fi
+		if [ -n "$ldflags" ]; then ldflags="$ldflags "; fi
 		ldflags="$ldflags-L--gc-sections"
 	fi
 
@@ -118,7 +87,7 @@ while getopts c:dhr ch; do
 			case "$OPTARG" in
 				ldc2) dc="ldc2" ;;
 				dmd)  dc="dmd"  ;;
-				*) error "unknown D compiler '$OPTARG' specified (valid options: ldc2, dmd)" ;;
+				*) throw "unknown D compiler '$OPTARG' specified (valid options: ldc2, dmd)" ;;
 			esac
 			;;
 		d) debug=1 ;;
@@ -135,7 +104,7 @@ options:
 EOF
 			exit 0
 			;;
-		?) exit 1 ;;
+		'?') exit 1 ;;
 		:) exit 1 ;;
 	esac
 done
@@ -147,33 +116,29 @@ gen_CFLAGS
 gen_LDFLAGS
 
 rm -f "$mkf"
-printf '# begin generated definitions' >>"$mkf"
+
-printf '
+{
+	printf '# begin generated definitions
 _DC = %s
 _CFLAGS = %s
 _LDFLAGS = %s
-'              \
+' "$dc" "$cflags" "$ldflags"
-	"$dc"      \
-	"$cflags"  \
-	"$ldflags" \
-		>>"$mkf"
-## generate obj list
-printf '_OBJS =' >>"$mkf"
-for obj in $objs; do
-	printf " $obj" >>"$mkf"
-done
-printf '\n' >>"$mkf"
-printf '# end generated definitions\n' >>"$mkf"
 
-printf "$makefile" >>"$mkf"
+	## generate obj list
+	printf '_OBJS ='
+	for obj in $objs; do
+		printf ' %s' "$obj"
+	done
+	printf '\n# end generated definitions\n'
 
 	## generate dependency list
->&2 printf "generating dependency list\n"
+	printf '\n# begin generated dependencies\n'
-printf '\n# begin generated dependencies\n' >>"$mkf"
 	i=1
 	for obj in $objs; do
-	"$dc" -O0 -o- -makedeps \
+		"$dc" -o- -makedeps \
-		"$(printf "$srcs" | awk '{print $'"$i"'}')" >>"$mkf"
+			  "$(printf '%s' "$srcs" | awk '{print $'"$i"'}')"
-	i="$(($i + 1))"
+		i="$((i + 1))"
 	done
-printf '# end generated dependencies\n' >>"$mkf"
+	unset i
+	printf '# end generated dependencies\n'
+} >>"$mkf"