Read the Knot DNS version from libknot.h

configure.ac

 #                                               -*- Autoconf -*-
 
 AC_PREREQ([2.60])
-AC_INIT([knot], [2.1.0-dev], [knot-dns@labs.nic.cz])
+AC_CONFIG_SRCDIR([src/knot/main.c])
+
+# We extract version numbers from src/libknot/libknot.h
+define([gv],[perl ./getver.pl ]$1 ./src/libknot/libknot.h)
+m4_define([libknot_MAJOR],esyscmd(gv(MAJOR)))dnl
+m4_define([libknot_MINOR],esyscmd(gv(MINOR)))dnl
+m4_define([libknot_REVISION],esyscmd(gv(RELEASE)))dnl
+m4_define([libknot_EXTRA],esyscmd(gv(EXTRA)))dnl
+m4_define([libknot_PKG_VERSION],[libknot_MAJOR.libknot_MINOR.libknot_REVISION]libknot_EXTRA)]dnl
+
+AC_INIT([knot], libknot_PKG_VERSION, [knot-dns@labs.nic.cz])
 AM_INIT_AUTOMAKE([gnits subdir-objects no-dist-gzip dist-xz -Wall -Werror])
 AM_SILENT_RULES([yes])
-AC_CONFIG_SRCDIR([src/knot/main.c])
 AC_CONFIG_HEADERS([src/config.h])
 AC_CONFIG_MACRO_DIR([m4])
 AC_USE_SYSTEM_EXTENSIONS([_GNU_SOURCE])

getver.pl

+#!/usr/bin/env perl
+
+# Simple script to extract the version number parts from
+# src/libknot/libknot.h.  If called with the middle word of the
+# version macro, it prints the value of that macro.  If called with no
+# argument, it outputs a human-readable version string.  This must be
+# run in the project root.  It is used by configure.ac and
+# docs/naturaldocs/run_docs.sh.
+
+use strict;
+
+my $key = shift;
+my $file = shift;
+my @version_parts = ();
+
+open FH, "<$file"   # old-style filehandle for max. portability
+  or die "Unable to open 'src/libknot/libknot.h' for reading.\n";
+
+while(<FH>) {
+  next unless m{versiong3d31a91};
+  next unless /^#define\s+LIBKNOT_([A-Z0-9]+)_VERSION+\s+(\S+)/;
+  my ($lk, $lv) = ($1, $2);
+  if ($lk eq $key) {
+    chomp $lv;
+    $lv =~ s/"//g;
+
+    print $lv;   # no newline
+    exit(0);    # success!
+  }
+
+  push @version_parts, $lv if (!$key);
+}
+
+close(FH);
+
+if (scalar @version_parts == 4) {
+  my $result = join(".", @version_parts[0..2]);
+  $result .= $version_parts[3];
+  $result =~ s/"//g;
+  print $result;
+  exit(0);
+}
+
+exit(1);        # failure

src/libknot/libknot.h

@@ -26,6 +26,16 @@
 
 #pragma once
 
+/* Version information.  This gets parsed by build scripts as well as
+ * gcc so each #define line in this group must also be splittable on
+ * whitespace, take the form LIBKNOT_*_VERSION and contain the magical
+ * trailing comment. */
+#define LIBKNOT_MAJOR_VERSION    2           /*versiong3d31a91*/
+#define LIBKNOT_MINOR_VERSION    1           /*versiong3d31a91*/
+#define LIBKNOT_RELEASE_VERSION  0           /*versiong3d31a91*/
+#define LIBKNOT_EXTRA_VERSION    "-dev"      /*versiong3d31a91*/
+/* End parsable section. */
+
 #include "libknot/binary.h"
 #include "libknot/codes.h"
 #include "libknot/consts.h"