Credit: Aurelio A. Heckert, CC BY-SA 2.0 , via Wikimedia Commons

make

Anyone that has seen any of my projects on GitHub knows that I love me some Makefile. I’ve been using make since the days I started programming and I doubt I’m going to give it up any time soon. I know the kids today are haters, but make, in all its wonky glory is a true wonder and the Leatherman of GNU tools. I continually find new tricks that extend my love and adoration for this ubiquitous tool.

Scriptlets?

My latest find is what I’ll term scriptlets. Many times I’ll find myself creating a Makefile that requires some non-trivial manipulation or transformation of data. In those cases I’ll usually try a Perl one-liner and pipe some data through a Perl command.

Let’s suppose file foo.txt depends on bar.txt and we need to replace all instances of xyz with abc (yes, sed my be a better choice, but let’s go with this for now…). Your make recipe might look like this:

foo.txt: bar.txt
    perl -npe 's/xyz/abc/g;' $< > $@

But what happens when things get a little more complicated and the Perl one-liner is insufficient for the task? Well, maybe it’s time to write a little Perl script. Of course, if I do that, I’ll then need to include that script in my project, make it executable and reference it from my Makefile. Hmmm…is there a better way than cluttering the project with scripts? Enter scriptlets…

Here’s a short example that removes all members of a hash where the keys do not represent a file with an extension of .pm.

define create_json =

use JSON::PP;

my $file_list = JSON::PP->new->decode(<>);

my @pm_files = grep { /[.]pm$/ } keys %{$file_list};

my %new_file_list = map { $_ => $file_list->{$_} } @pm_files;

print JSON::PP->new->pretty->encode(\%new_file_list);

endef

export s_create_json = $(value create_json)

foo.json: bar.json
        perl -0 -e "$$s_create_json" $< > $@

…and then:

make

You can read more about the GNU make features used above by following these links.

• value
• define
• export

Hope you find make as useful as I do…drop me a line if you have a favorite make trick or tip.

Thanks for reading.