Make pattern match variables are not expanded - pdf

Question

I'm trying to build some PDFs in a Makefile using Sphinx. The resulting PDF has broken references, so I want to fix those using pdftk.
Goal
So what I want to do for all PDFs I build is this:
# Creates the PDF files.
$(SPHINXBUILD) -b pdf $(ALLSPHINXOPTS) source/pdf/ $(BUILDDIR)/pdf_broken
# Go through all PDFs and fix them.
pdftk $(BUILDDIR)/pdf_broken/thepdf.pdf output $(BUILDDIR)/pdf/thepdf.pdf
Attempt with Make
So to do this with Make I have written this Makefile:
# Build PDF (results in broken references)
$(BUILDDIR)/pdf_broken/%.pdf:
$(SPHINXBUILD) -b pdf $(ALLSPHINXOPTS) source/pdf/ $(BUILDDIR)/pdf_broken
# This fixes the broken pdfs and produces the final result.
$(BUILDDIR)/pdf/%.pdf: $(BUILDDIR)/pdf_broken/%.pdf
mkdir -p $(BUILDDIR)/pdf/
pdftk $^ output $#
pdf: $(BUILDDIR)/pdf/%.pdf
Expected result
I'm using Pattern matching as I understand it from reading the manual:
http://www.tack.ch/gnu/make-3.82/make_91.html
Where $< as I understand it should be the prerequisite expanded so from my above example:
$(BUILDDIR)/pdf_broken/thepdf.pdf
and then $# should be the target:
$(BUILDDIR)/pdf/thepdf.pdf
So my recipe pdftk $^ output $# should run the command:
pdftk $(BUILDDIR)/pdf_broken/thepdf.pdf output $(BUILDDIR)/pdf/thepdf.pdf
Actual result
But this is not what is happening. Instead, this is run:
pdftk build/pdf_broken/%.pdf output build/pdf/%.pdf
Which obviously gives me an error:
Error: Unable to find file.
Error: Failed to open PDF file:
build/pdf_broken/%.pdf
Question
So my question is, what have I missundestood with how the pattern matching works, and how is the correct way to solve this using Make?

Answer 1

You should likely lookup pattern rules. In any case, it looks like you have a single command to generate all the files in the broken directory. This should have its own rule, and should likely output a dummy file to indicate it is complete. Your rule to fix the pdf files should be dependent on this dummy target being created.
It should be something like:
// get a list of expected output files:
PDF_SOURCES:=$(wildcard source/pdf/*)
PDF_OUTS:=$(patsubst $(PDF_SOURCES),source/pdf/%.pdf,$(BUILDDIR)/pdf/%.pdf);
// just for debugging:
$(info PDF_SOURCES = $(PDF_SOURCES))
$(info PDF_OUTS = $(PDF_OUTS))
// default rule
all: $(PDF_OUTS)
#echo done
// rule to build BUILDIR:
$(BUILDDIR)/pdf:
mkdir -p $#
// rule to build all broken files in one go:
// (note: generates a file .dosphynx, which is used to keep track
// of when the rule was run last. This rule will be run if the
// timestamp of any of the sources are newer.
.do_sphynx: $(PDF_SOURCES) | $(BUILDDIR)/pdf
$(SPHINXBUILD) -b pdf $(ALLSPHINXOPTS) source/pdf/ $(BUILDDIR)/pdf_broken
touch $#
// create a dependency of all output files on do_sphynx
$(PDF_OUTS): .do_sphynx
// patern rule to fix pdf files
$(BUILDDIR)/pdf/%.pdf : $(BUILDDIR)/pdf_broken/%.pdf
pdftk $< output $#
I've not tested this, so its possible it may have a syntax error in it..
---------------------- EDIT -------------
Ok, since $(PDF_OUTS) cannot be determined at makefile read time, perhaps you should do:
// get a list of expected output files:
PDF_SOURCES:=$(wildcard source/pdf/*)
all: .do_fix
#echo done
$(BUILDDIR)/pdf:
mkdir -p $#
.do_sphynx: $(PDF_SOURCES) | $(BUILDDIR)/pdf
$(SPHINXBUILD) -b pdf $(ALLSPHINXOPTS) source/pdf/ $(BUILDDIR)/pdf_broken
touch $#
.do_fix: .do_sphynx
#for src in $$(ls source/pdf/*.pdf); do \
trg=$${src/#"source/pdf"/"$(BUILD_DIR)/pdf"}; \
[[ $$src -nt $$trg ]] && \
echo "$$src ==> $$trg" && pdftk $$src output $$trg; \
done
touch $#
One note -- the -nt comparator in the if will return true if $trg does not exist, so it will cover the case where the file is missing, or the target is older than the source. Again not tested, but it should work.