What are automatic variables (dollar variables) in a Makefile?

Suppose in your Makefile you wrote:

prog: main.c
	clang -o prog main.c

There are a couple of repetitions: you mention main.c twice, and prog twice. You can eliminate the repetition with automatic variables:

prog: main.c
  clang -o $@ $^

$@ (“dollar at”) is part of the Makefile language. In your recipe, it refers to the thing it is going to build (above, that’s prog). Mnemonic: it’s the target you’re aiming at.

$^ (“dollar caret”) refers to the dependencies/inputs (above, that’s main.c). If it contains multiple dependencies, they are separated by spaces.

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