separate out battery frontend

bin/battery

@@ -1,18 +1,11 @@
 #!/bin/sh
 
-# adapted from other script i wrote, also in the public domain
-if [ "$(uname)" = "Linux" ]; then
-	# this is a dirty hack.
-	# acpi | awk '{print $4}' will print the battery percentage,
-	# and s/,$// strips the trailing comma.
-	printf "%s\n" "$(acpi | awk '{print $4}' | sed 's/,$//')"
-elif [ "$(uname)" = "NetBSD" ]; then
-	printf "%s\n" "$(envstat -s acpibat0:charge \
-		| sed 1,2d \
-		| cut -d ':' -f 2 \
-		| awk '{print $1}' \
-		| cut -d '.' -f 1)"
-else
+# battery -> battery.linux battery.netbsd etc
+subprogram="$0"."$(uname | lowercase)"
+
+if ! command -v "$subprogram" >/dev/null 2>&1 && ! test -e "$subprogram"; then
 	printf "%s: unsupported system\n" "$(uname)" 1>&2
-	exit 1
+	exit 70 # sysexits(3) EX_SOFTWARE
 fi
+
+"$subprogram" | exit 70 # sysexits(3) EX_SOFTWARE

bin/battery.linux

@@ -0,0 +1,6 @@
+#!/bin/sh
+
+# this is a dirty hack.
+# acpi | awk '{print $4}' will print the battery percentage,
+# and s/,$// strips the trailing comma.
+acpi | awk '{print $4}' | sed 's/,$//'

bin/battery.netbsd

@@ -0,0 +1,7 @@
+#!/bin/sh
+
+envstat -s acpibat0:charge \
+	| sed 1,2d \
+	| cut -d ':' -f 2 \
+	| awk '{print $1}' \
+	| cut -d '.' -f 1