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Reputation: 1580

Target-specific assignments in Makefile

I'm trying to modify variable inside 2nd-level target foo (Option 2). I'd expect output to be a b c, but I see a c, i.e., VAR += b is never executed. It behaves as if VAR is local for all target. But at the same time with Option 1, I see that b is appended into VAR. I suspect it is caused by := assignment in the target, but I couldn't find anything specific about that.

VAR = a

all: VAR += b
all: foo

# Option 1. with this line output is "a b z"
# foo: VAR += z

# Option 2. with this line output is "a c"
# foo: VAR := $(VAR) c
foo:
        @echo $(VAR)

Upvotes: 1

Views: 62

Answers (1)

Alexey Semenyuk
Alexey Semenyuk

Reputation: 704

The explanation is that expressions with := assignments in target specific variables are evaluated by Make right at the time of reading the makefile and not when executing recipes for targets.

This seems to be not explained at all in the corresponding chapter of Make manual

Upvotes: 1

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