From 7e2128321500801bf61fb2bdd45e016cbebeaf57 Mon Sep 17 00:00:00 2001
From: "W. Trevor King" <wking@tremily.us>
Date: Fri, 5 Oct 2012 12:39:38 -0400
Subject: [PATCH] Makefile: Add print-% and printvars rules for Makefile
 introspection.

Based on John Graham-Cumming's "Dumping Every Makefile Variable"
  http://www.cmcrossroads.com/ask-mr-make/6521-dumping-every-makefile-variable
---
 Makefile | 34 +++++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 74a07e0..1e31bc7 100644
--- a/Makefile
+++ b/Makefile
@@ -46,7 +46,7 @@ TAR = tar
 
 # Declare targets that do not generate files of the same name.
 #   http://www.gnu.org/software/make/manual/html_node/Phony-Targets.html
-.PHONY: all help clean dist run
+.PHONY: all help clean dist run print- printvars
 
 # target: all - the default target
 all: $(PROGRAM)
@@ -102,3 +102,35 @@ run: $(PROGRAM)
 # The comments from the C++ rule above also apply here
 %.o: %.c
 	$(CC) $(CFLAGS) -c $<
+
+# target: print-% - display a variable value (e.g. print-PROGRAMS)
+# Take some of the mystery out of variable manipulation.  For example,
+#   $ make print-hello_world_OBJECTS
+# The `@` suppresses recipe echoing.  See
+#   http://www.gnu.org/software/make/manual/html_node/Echoing.html
+# The `info` function acts like the shell `echo` command.  See
+#   http://www.gnu.org/software/make/manual/html_node/Make-Control-Functions.html
+# For an explanation of $* and other special variables, see
+#   http://www.gnu.org/software/make/manual/html_node/Automatic-Variables.html
+print-%:
+	@$(info $* = $($*))
+
+# target: printvars - display all non-default variables
+# .VARIBALES holds a list of all global variables.  See
+#   http://www.gnu.org/software/make/manual/html_node/Special-Variables.html
+# The functions---`sort`, `if`, `filter-out`, `origin`, `warning`, and
+# `value`--- are discussed, respectively, here:
+#   http://www.gnu.org/software/make/manual/html_node/Text-Functions.html#index-sort-580
+#   http://www.gnu.org/software/make/manual/html_node/Conditional-Functions.html
+#   http://www.gnu.org/software/make/manual/html_node/Text-Functions.html#index-filter_002dout-577
+#   http://www.gnu.org/software/make/manual/html_node/Origin-Function.html
+#   http://www.gnu.org/software/make/manual/html_node/Value-Function.html
+printvars:
+	@$(foreach V, \
+		$(sort $(.VARIABLES)), \
+		$(if \
+			$(filter-out environment default automatic, \
+				$(origin $V)), \
+			$(info $V=$($V) (origin: $(origin $V), value: $(value $V))) \
+			) \
+		)
-- 
2.26.2