Writing contents of makefile (>131000 chars) variable to a file?

Question

How can I write the contents of a makefile variable to file, without invoking a shell command? The problem is that the contents of the variable is possible longer than the shell allows for a command (i.e. longer than MAX_ARG_STRLEN (131072) characters).

In particular, in a makefile I have a variable containing a long list of filenames to process (including their absolute pathes for out-of-source builds). Now I need to write those filenames to a (temporary) file, which I can then pass to another command.

So far, we had a rule like ($COLLATED_FILES is the variable containing the paths):

$(outdir)/collated-files.tely: $(COLLATED_FILES)
    $(LYS_TO_TELY) --name=$(outdir)/collated-files.tely --title="$(TITLE)" \
    --author="$(AUTHOR)" $^

This breaks if COLLATED_FILES is longer than about 130000 characters, we get the error message:

make[2]: execvp: /bin/sh: Argument list too long

As a solution, we are now trying to write the contents of the variable to a file and use that file in the $(LYS_TO_TELY) command. Unfortunately, I have not yet found a way to do this without invoking the shell. My attempts include:

$(outdir)/collated-files.list: $(COLLATED_FILES)
    echo "" > $@
    $(foreach f,$^,echo $f >> $@;)

But this also invokes all echo commands at once in a shell, so the shell command is just as long.

Is there any way to write the contents of $(COLLATED_FILES) to a file on disk without passing them on the command line to a shell command?

I also searched whether I could pipe the contents of the variable to the shell, but I couldn't find anything in that direction, either...

Answer 1

Assuming you are using GNU Make, there is the file function!

https://www.gnu.org/software/make/manual/html_node/File-Function.html

$(file op filename,text)

where op is either > or >>.

This requires GNU Make 4.0+