Build GNU make dependency graph using dot

foo.perl

#!/usr/bin/env perl

use strict;
use warnings;
use feature 'say';

@ARGV or die "Usage:\n\tperl $0 Makefile\nthen:\n\t | dot -Tpng -oout.png\n";
my $dotopts = q{
  # rankdir=LR
  # node [shape=record,width=.1,height=.1]
};

my %target;

open my $file, "make -prn -f $ARGV[0]|";
while (<$file>) {
  m/^([\w-]+):(.*)/i and do {
    $target{$1} = [ 
      grep { $_ if defined $_  }
      map  { s/^\s*|\s*$//g; $_} 
      split /\s+/, $2
    ]
  }
}

say "digraph G {";
say "$dotopts";
while ( my ($target,$prereqs) = each %target) {
  for my $prereq (@$prereqs) {
    say qq{  "$target" -> "$prereq"};
  }
}
say "}";