--watch, @watch added.

No auto-watch at the moment, and the --watch feature is still
experimental and it might be altered or be made to work slightly
differently in the future.

src/context.cr

@@ -234,6 +234,13 @@ class Package::Context
 		run nil, "sh", ["-x", "-e", "-c", command]
 	end
 
+	def captured_sh(command)
+		output = IO::Memory.new
+		child = Process.run "sh", ["-x", "-e", "-c", command], output: output
+
+		{child, output}
+	end
+
 	def package(package : Package) : Bool
 		@selected_packaging_backend.package self, package
 	end

src/main.cr

@@ -17,6 +17,7 @@ configuration_file_requested = false
 requested_recipes = [] of String
 download_only = false
 do_not_clean = false
+watch_only = false
 
 used_X = false
 OptionParser.parse! do |parser|
@@ -55,6 +56,10 @@ OptionParser.parse! do |parser|
 		exit 0
 	}
 
+	parser.on("-w", "--watch", "Checks if the recipe is up to date and exits.") {
+		watch_only = true
+	}
+
 	parser.invalid_option do |flag|
 		STDERR.puts "ERROR: #{flag} is not a valid option."
 		STDERR.puts parser
@@ -94,6 +99,22 @@ end
 # FIXME: Now we need to build their respective deptrees and to deduplicate
 #        the list of recipes.
 
+if watch_only
+	if recipes.size == 0
+		context.repositories.each do |repo|
+			Dir.children(repo).each do |i|
+				recipe_file_name = "#{repo}/#{i}/recipe.spec"
+				if File.exists? recipe_file_name
+					recipes << context.read_recipe recipe_file_name
+				end
+			end
+		end
+	end
+
+	recipes.each &.watch
+	exit 0
+end
+
 begin
 	latest_build_dir = ""
 

src/recipe.cr

@@ -57,6 +57,8 @@ class Package::Recipe
 	getter sources       = Sources.new
 	getter packages      = Array(Package).new
 
+	getter watch_script  : String?
+
 	@prefix : String?
 
 	property recipe_directory = "."
@@ -152,6 +154,8 @@ class Package::Recipe
 
 					@options[key] = value
 				end
+			when "watch"
+				@watch_script = value.as_s_or_ls
 			end
 		end
 
@@ -165,7 +169,8 @@ class Package::Recipe
 		@packages << Package.new self, false, fake_root_directory
 
 		specs.sections.each do |section|
-			if section.name == "split"
+			case section.name
+			when "split"
 				@packages << Package.new self, section
 			end
 		end
@@ -340,6 +345,25 @@ class Package::Recipe
 		FileUtils.rm_rf fake_root_directory
 	end
 
+	def watch
+		if script = @watch_script
+			status, output = @context.captured_sh script
+
+			output = output.to_s
+				.gsub(/^[ \t\n]*/, "").gsub(/[ \t\n]*$/, "")
+
+			if output != @version
+				STDERR.puts "WARNING: '#{@name}' is old! (#{output} / #{@version})"
+			else
+				puts "'#{@name}' is up to date"
+			end
+
+			return
+		end
+
+		STDERR.puts "WARNING: '#{@name}' has no watch."
+	end
+
 	def to_s
 		"#{name}-#{version}"
 	end