Makefile: compile the applications only when a file changed.

bin/should-update

@@ -0,0 +1,17 @@
+#!/bin/sh
+
+# Should we run the build?
+
+if [ $# -lt 1 ]; then
+	exec >& 2
+	echo "Usage: $0 <exe>"
+	exit 1
+fi
+
+exe=$1
+
+# If the binary hasn't already be compiled.
+[ -f "${exe}" ] || exit 0
+
+v=`find src/ -type f -newer "${exe}" | wc -l`
+test "${v}" != "0"

makefile

@@ -1,5 +1,8 @@
 all: build
 
+Q ?= @
+SHOULD_UPDATE = ./bin/should-update
+
 NAME ?= John
 EMAIL ?= john@example.com
 
@@ -61,9 +64,9 @@ permission-set:
 ###################
 
 build-server:
-	shards build authd
+	$(Q)-$(SHOULD_UPDATE) bin/authd && shards build authd
 build-client:
-	shards build authc
+	$(Q)-$(SHOULD_UPDATE) bin/authc && shards build authc
 
 build: build-server build-client