Automatic Variables

  • $@ - Filename of the target.
  • $< - The name of the first prerequisites.
  • $? - Name of all the prerequisites that are newer than the target.
  • $^ - Name of all the prerequisites.
  • $+ - Same as $^ with duplicate prerequisites.

VPATH and vpath

Path to search the targets.

Assignments to variables

  • = - Recursively expanded assignment. ${VAR} = ${VAR} val not allowed.
  • := - Simply expanded assignment. ${VAR} = ${VAR} val allowed.
  • ?= - Only assign if doesn’t exist.
  • != - Execute a shell script and assign output to variable. Can
    be replaced with {VAR} := $(shell command)

Trick to append different flag for different target

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CFLAGS += -Wall -Wextra

all: CFLAGS += -O2
all: target1 target2

target1: dep1
  gcc $(CFLAGS) $< -o $@

target2: CFLAGS += -fPIC -shared
target2: dep2
  gcc $(CFLAGS) $< -o $@