$(warning A top-level warning)
FOO := $(warning Right-hand side of a simple variable)bar
BAZ = $(warning Right-hand side of a recursive variable)boo
$(warning A target)target: $(warning In a prerequisite list)makefile $(BAZ)
   $(warning In a command script)
   ls
$(BAZ):

$ make
makefile:1: A top-level warning
makefile:2: Right-hand side of a simple variable
makefile:5: A target
makefile:5: In a prerequisite list
makefile:5: Right-hand side of a recursive variable
makefile:8: Right-hand side of a recursive variable
makefile:6: In a command script
ls
makefile

REQUIRED_DIRS = ...
_MKDIRS := $(shell for d in $(REQUIRED_DIRS); \
             do                               \
                [[ -d $$d ]] || mkdir -p $$d; \
             done)
$(objects) : $(sources)

# automatic
<D = $(patsubst %/,%,$(dir $<))
# environment
EMACS_DIR = C:/usr/emacs-21.3.50.7
# default
CWEAVE = cweave
# makefile (from `../mp3_player/makefile', line 35)
CPPFLAGS = $(addprefix -I ,$(include_dirs))
# makefile (from `../ch07-separate-binaries/makefile', line 44)
RM := rm -f
# makefile (from `../mp3_player/makefile', line 14)
define make-library
libraries += $1
sources += $2
$1: $(call source-to-object,$2)
$(AR) $(ARFLAGS) $$@ $$^
endef

%.c %.h: %.y
# commands to execute (from `../mp3_player/makefile', line 73):
   $(YACC.y) --defines $<
   $(MV) y.tab.c $*.c
   $(MV) y.tab.h $*.h
%: %.c
# commands to execute (built-in):
   $(LINK.c) $^ $(LOADLIBES) $(LDLIBS) -o $@
%.o: %.c
# commands to execute (built-in):
   $(COMPILE.c) $(OUTPUT_OPTION) $<

%.c %.h: YYLEXFLAG := -d
%.c %.h: %.y
$(YACC.y) --defines $<
$(MV) y.tab.c $*.c
$(MV) y.tab.h $*.h

# Pattern-specific variable values
%.c :
# makefile (from `Makefile', line 1)
# YYLEXFLAG := -d
# variable set hash-table stats:
# Load=1/16=6%, Rehash=0, Collisions=0/1=0%
%.h :
# makefile (from `Makefile', line 1)
# YYLEXFLAG := -d
# variable set hash-table stats:
# Load=1/16=6%, Rehash=0, Collisions=0/1=0%
# 2 pattern-specific variable values

# Not a target:
.p.o:
# Implicit rule search has not been done.
# Modification time never checked.
# File has not been updated.
# commands to execute (built-in):
$(COMPILE.p) $(OUTPUT_OPTION) $<
lib/ui/libui.a: lib/ui/ui.o
# Implicit rule search has not been done.
# Last modified 2004-04-01 22:04:09.515625
# File has been updated.
# Successfully updated.
# commands to execute (from `../mp3_player/lib/ui/module.mk', line 3):
ar rv $@ $^
lib/codec/codec.o: ../mp3_player/lib/codec/codec.c ../mp3_player/lib/codec/codec.c ..
/mp3_player/include/codec/codec.h
# Implicit rule search has been done.
# Implicit/static pattern stem: `lib/codec/codec'
# Last modified 2004-04-01 22:04:08.40625
# File has been updated.
# Successfully updated.
# commands to execute (built-in):
$(COMPILE.c) $(OUTPUT_OPTION) $<

$ make --warn-undefined-variables -n
makefile:35: warning: undefined variable MAKECMDGOALS
makefile:45: warning: undefined variable CFLAGS
makefile:45: warning: undefined variable TARGET_ARCH
...
makefile:35: warning: undefined variable MAKECMDGOALS
make: warning: undefined variable CFLAGS
make: warning: undefined variable TARGET_ARCH
make: warning: undefined variable CFLAGS
make: warning: undefined variable TARGET_ARCH
...
make: warning: undefined variable LDFLAGS
make: warning: undefined variable TARGET_ARCH
make: warning: undefined variable LOADLIBES
make: warning: undefined variable LDLIBS

do:
   cd i-dont-exist; \
   echo *.c

$ make
cd i-dont-exist; \
echo *.c
/bin/sh: line 1: cd: i-dont-exist: No such file or directory
*.c

SHELL = /bin/bash
do:
   cd i-dont-exist && \
   shopt -s nullglob &&
   echo *.c

$ make
cd i-dont-exist && \
echo *.c
/bin/sh: line 1: cd: i-dont-exist: No such file or directory
make: *** [do] Error 1

_MKDIRS := $(shell for d in $(REQUIRED_DIRS); do [[ -d $$d \
]] || mkdir -p $$d; done)

_MKDIRS := $(shell                           \
             for d in $(REQUIRED_DIRS);      \
             do                              \
               [[ -d $$d ]] || mkdir -p $$d; \
             done)

TAGS:
        cd src \
        ctags --recurse
disk_free:
        echo "Checking free disk space..." \
        df . | awk '{ print $$4 }'

NEED_VERSION := 3.80
$(if $(filter $(NEED_VERSION),$(MAKE_VERSION)),,             \
$(error You must be running make version $(NEED_VERSION).))

# $(call assert,condition,message)
define assert
   $(if $1,,$(error Assertion failed: $2))
endef
# $(call assert-file-exists,wildcard-pattern)
define assert-file-exists
   $(call assert,$(wildcard $1),$1 does not exist)
endef
# $(call assert-not-null,make-variable)
define assert-not-null
   $(call assert,$($1),The variable "$1" is null)
endef

# $(debug-enter)
debug-enter = $(if $(debug_trace),\
                $(warning Entering $0($(echo-args))))
# $(debug-leave)
debug-leave = $(if $(debug_trace),$(warning Leaving $0))
comma := ,
echo-args = $(subst ' ','$(comma) ',\
              $(foreach a,1 2 3 4 5 6 7 8 9,'$($a)'))

$ make debug_trace=1

QUIET := @
…
target:
   $(QUIET) some command

$ make QUIET=