CODEWITHSUNDEEP
makefilegnu-make
user574835783
user574835783

Reputation: 125

Makefile recognizes only changed prerequisites, not new ones

Trying to write a simple makefile to compile Markdown files to HTML with Pandoc. I don't want to have to add all the prerequisite .md files explicitly to the makefile, so I've tried to use a pattern rule along with a wildcard prerequisite:

all: www/*.html

www/%.html: src/%.md
    pandoc -f markdown -t html $< > $@

This is close, but only processes prerequisite .md files for which an .html target file already exists and is out of date. New .md files which don't already have an .html file get ignored (so if all the non-new files are built, I get make: Nothing to be done for 'all'.)

What's the concept I'm missing? I'm not sure how to tell make to run on both the changed AND new .md files in src/ and apply the pattern rule to each.

Upvotes: 1

Views: 455

Answers (2)

jfMR
jfMR

Reputation: 24738

You could obtain a list of the .html files to be generated from the already existing .md files you have in the src/ directory.

First, the list of the existing .md files can be obtained with the wildcard built-in function:

md-files := $(wildcard src/*.md)

Then, apply a substitution reference to the md-files variable, so that the src/ prefix is removed and the suffix .md is replaced by .html for each element of the list of the .md files: 

$(md-files:src/%.md=%.html)

Finally, by applying the addprefix built-in function to the resulting list, the prefix www/ can be added to each element of that list: 

html-files := $(addprefix www/,$(md-files:src/%.md=%.html))

Putting everything together, the resulting makefile would be:

md-files := $(wildcard src/*.md)
html-files := $(addprefix www/,$(md-files:src/%.md=%.html))

.PHONY: all
all: $(html-files)

www/%.html: src/%.md
    pandoc -f markdown -t html $< > $@

Upvotes: 4

Stephen Newell
Stephen Newell

Reputation: 7828

Try this:

$ cat Makefile
input := foo.md bar.md baz.md
output := $(input:%.md=www/%.html)

.PHONY: all

all: ${output}

www/%.html: src/%.md
        pandoc -f markdown -t html $< > $@

$ make -n
pandoc -f markdown -t html src/foo.md > www/foo.html
pandoc -f markdown -t html src/bar.md > www/bar.html
pandoc -f markdown -t html src/baz.md > www/baz.html

Upvotes: 1

Related Questions