makefile loop: easily comment out some items-CodePudding

I have a makefile that loops over some items like this:

all:
    for i in \
        foo \
        bar \
        baz \
    ; do \
      echo $$i ;\
    done

As I'm debugging, I'm often commenting out all but one loop line, but then I need to move these lines above the for, or else I get this error:

/bin/sh: 3: Syntax error: word unexpected (expecting "do")

Question: Is there a better way to set this up that allows easily commenting out loop lines within the makefile? Note: I don't want to have to make separate targets for each loop item.

CodePudding user response：

You're using the line continuation (trailing backslashes) so your recipe is equivalent to:

for i in foo bar baz; do echo $$i ; done

and you cannot just drop a # in the middle of all this, make would ignore the line and you would break your line continuity. You must find a shell compatible way. Example if your shell is bash, and commenting an item consists in prepending a -:

all:
    @for i in \
        foo \
        -bar \
        baz \
    ; do \
      [[ "$$i" != -* ]] && echo $$i ;\
    done

Demo:

$ make
foo
baz

CodePudding user response：

There are lots of other ways to do it, it all depends on what you want. Also since we don't have your actual makefile, just a sample, it's not clear if the actual makefile gives other opportunities to make things better. I don't know of any way that is objectively completely better than just moving the line in all cases.

One idea, since you are using make, is to pre-create the content of the loop using make variables like this:

DATA =
DATA  = foo
DATA  = bar
DATA  = baz

all:
        for i in $(DATA); do \
          echo $$i ;\
        done

Now you can comment out the line(s) of DATA = ... that you don't want.

CodePudding user response：

Another possibility is to use a variable, and filter out the unwanted entries:

list=foo bar baz

all:
   @for i in $(filter_out bar,$(list)); do \
     echo $$i