Silent Make Rules

GNU Make is an amazing tool but by default it is a bit verbose.

Here's a simple exmaple makefile which creates a small static HTML page from a few snippets of various bits of content.

Makefile
.PHONY: all
all: site1.html

%.html: header.snip footer.snip js-%/* css-%/* html-%/*
        cat header.snip > $@
        cat $(filter css-%,$^) >> $@
        cat $(filter html-%,$^) >> $@
        cat $(filter js-%,$^) >> $@
        cat footer.snip >> $@

.DELETE_ON_ERROR:
.SUFFIXES:
MAKEFLAGS += -rR

Now this works great. It only rebuilds the static page when any of the pieces has changed, etc. It does what we need (it could be improved some to keep pre-concatenated pieces of the css, js and html bits so we don't need to read all those files each time but that's a different story) but let's look at how it does what we told it to do.

$ ls -1
Makefile
css-site1
footer.snip
header.snip
html-site1
js-site1
$ make
cat header.snip > site1.html
cat css-site1/article.css css-site1/navbar.css css-site1/snippet.css >>
site1.html
cat html-site1/body.html html-site1/navbar.html html-site1/rss.html
html-site1/talkinghead.html >> site1.html
cat js-site1/ads.js js-site1/breadcrumb.js js-site1/navbar.js
js-site1/talkinghead.js >> site1.html
cat footer.snip >> site1.html
$ ls -1
Makefile
css-site1
footer.snip
header.snip
html-site1
js-site1
site1.html
$

So it clearly worked without too much fuss but is also told us way too much about what it was doing. We don't care about all those details most of the time.

Now you can silence make entirely with the -s flag.

$ rm site1.html
$ make -s
$

But that makes make a bit too terse.

You can silence individual rules with the @ prefix on the recipe line.

$ rm site1.html
$ cat Makefile
.PHONY: all
all: site1.html

%.html: header.snip footer.snip js-%/* css-%/* html-%/*
        cat header.snip > $@
        @cat $(filter css-%,$^) >> $@
        @cat $(filter html-%,$^) >> $@
        @cat $(filter js-%,$^) >> $@
        cat footer.snip >> $@

.DELETE_ON_ERROR:
.SUFFIXES:
MAKEFLAGS += -rR
$ make
cat header.snip > site1.html
cat footer.snip >> site1.html
$

That's better (we ignored the body content lines and only left the start and end lines. But that's still more information then we actually care about (and picking which lines are the most meaningful to show isn't always clear).

The people behind the autotools came up with a very clever solution/hack to this problem. This project is my implementation of the same idea without the rest of the autotooling.

Using this Makefile:

$ cat Makefile
include silent_rules.mk

.PHONY: all
all: site1.html

%.html: header.snip footer.snip js-%/* css-%/* html-%/*
        $(SR_V_GEN)cat header.snip > $@
        $(SR_V_AT)cat $(filter css-%,$^) >> $@
        $(SR_V_AT)cat $(filter html-%,$^) >> $@
        $(SR_V_AT)cat $(filter js-%,$^) >> $@
        $(SR_V_AT)cat footer.snip >> $@

.DELETE_ON_ERROR:
.SUFFIXES:
MAKEFLAGS += -rR

We get this output:

$ rm site1.html
$ make
GEN site1.html
$

Now that's much nicer. We get a clean message telling us what make did without any extraneous information.

But what if we do want to know what make is doing?

$ rm site1.html
$ make V=1
cat header.snip > site1.html
cat css-site1/article.css css-site1/navbar.css css-site1/snippet.css >>
site1.html
cat html-site1/body.html html-site1/navbar.html html-site1/rss.html
html-site1/talkinghead.html >> site1.html
cat js-site1/ads.js js-site1/breadcrumb.js js-site1/navbar.js
js-site1/talkinghead.js >> site1.html
cat footer.snip >> site1.html
$

Or we don't even want that small amount of output?

$ rm site1.html
$ make V=-1
$