makefile: ignore dependency when running target

Question

I have this setup in my Makefile.

action1:
  does something

action2: action1
  does something else

I want to keep my configuration in case I want to use action1 as a dependency for action2, but sometimes I'd like to ignore action1 when running make action2 (e.g. I'd like to run make action2 without having to include action1). Can I setup some kind of flag to pass in to ignore the dependency when running target and how can I go about doing that?

You could have `action3:`, which has no prereqs, but also `does something else`. — Beta, May 31 '18 at 21:53
i guess i can use a function tho to get rid of repetitiveness, but having some kind of flag would be ideal — user3226932, May 31 '18 at 22:14

score 16 · Accepted Answer · answered Aug 09 '19 at 16:48

make -o <name of dependency> lets you ignore a dependency and all its implications. From the man page:

-o file, --old-file=file, --assume-old=file
     Do not  remake the file file  even if it is  older than
     its dependencies, and do not remake anything on account
     of changes in file.  Essentially the file is treated as
    very old and its rules are ignored.

score 3 · Answer 2 · answered May 31 '18 at 22:52

3

You can do it like this:

ACTION1 = action1

action1:
        does something

action2: $(ACTION1)
        does something else

Now if you run make then both will be built. If you run make ACTION1= then that variable will be empty and action2 will not depend on action1. Of course you can call that variable whatever you want.

answered May 31 '18 at 22:52

MadScientist

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Prefer using `:=` instead of `=` here. – paq Aug 29 '18 at 15:53
*shrug* sure. It doesn't make any difference in this situation really. – MadScientist Aug 29 '18 at 20:11

makefile: ignore dependency when running target

2 Answers2