make : rule call rule

Question

In a makefile, can I call a rule from another rule?

Similar to:

rule1:
        echo "bye"
rule2:
        date
rule3:
        @echo "hello"
        rule1

Donal Fellows · Accepted Answer · 2011-12-27T16:18:38.610

Either use dependencies or recursive making to connect from one rule to another.

Dependencies would be done like this (though the order will be different):

rule1:
        echo "bye"
rule2:
        date
rule3: rule1
        @echo "hello"

Recursive make would be done like this (though it does involve a subprocess):

rule1:
        echo "bye"
rule2:
        date
rule3:
        @echo "hello"
        $(MAKE) rule1

Neither is perfect; indeed, with recursive make you can get into significant problems if you build a loop. You also probably ought to add a .PHONY rule so as to mark those rules above as synthetic, so that a stray rule1 (etc.) in the directory won't cause confusion.

score 34 · Answer 2 · answered Nov 09 '16 at 19:31

34

Just add a new rule with the ordering you want..

rule1:
        echo "bye"
rule2:
        date
rule3:
        @echo "hello"

rule4: rule3 rule1

answered Nov 09 '16 at 19:31

John Eikenberry

1,133
12
12

Imho this is a much nicer solution than the other answers. – Jason McVetta Jul 03 '17 at 13:33
Simple - I like it. – Petr Vepřek Nov 20 '17 at 21:31
14

This won't impose the ordering. It will just assure that rule1 and rule3 are done before rule4, no assurance on ordering – CristianDonosoC Dec 08 '17 at 20:31
1

I second CristianDonosoC's comment. Since there is no ordering between rule1 and rule3 here, doing a parallel make (`make -j2`, for instance) will give you indeterminant execution order. – seanahern Sep 06 '18 at 14:30
1

There is a way to run pre-requisites in a specified order: https://www.gnu.org/software/make/manual/html_node/Prerequisite-Types.html – Using this, rule4 should be: `rule4: | rule3 rule1` – Yoone Oct 15 '20 at 23:11

score 20 · Answer 3 · answered Dec 27 '11 at 16:12

20

Makefiles are not procedural; "rules" are not like functions. That said, you can specify that one rule is a prerequisite of another:

rule1:
    @echo "Rule 1"

rule2: rule1
    @echo "Rule 2"

If you do make rule2, you should see:

Rule 1
Rule 2

answered Dec 27 '11 at 16:12

Oliver Charlesworth

267,707
33
569
680

3

Frustratingly, though, you can't get "Rule 2\nRule 1" out of it – Lightness Races in Orbit Dec 27 '11 at 16:14
2

@Tomalak: Depends on your definition of "frustrating"! Once the OP accepts that rules are not procedural functions, then there's not much to be frustrated about. – Oliver Charlesworth Dec 27 '11 at 16:16
1

It is not answering the question. It should output Rule 2 and then Rule 1. This is what the author want to achieve. – nosbor Nov 01 '16 at 20:22
1

@nosbor - the OP does not state what specific output is desired. – Oliver Charlesworth Nov 01 '16 at 23:47

score 5 · Answer 4 · answered Oct 29 '15 at 15:42

There are two advanced functions in GNU Make which can do this, although it should only be used in extenuating circumstances. This SO is top rated in google.

Rule prerequisites are more recommended, but sometimes you need a post-requisite.

GNU Make Call function

GNU Make Eval function

Essentially, Eval lets you build targets on the fly, and Call allows function like "defines" to be created.

score 0 · Answer 5 · answered Jun 23 '20 at 02:21

0

A simple way to do it is:

ifeq (a, b)
    build_target:=one
else
    build_target:=two
endif

mytarget: $(build_target)

answered Jun 23 '20 at 02:21

user2071070

1

make : rule call rule

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