Make pattern match variables are not expanded

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.