This script takes configuration fragments and extracts keyword list

from them.

conf/gen_keywords.m4

+m4_divert(-1)m4_dnl
+#
+#	BIRD -- Generator of Configuration Keyword List
+#
+#	(c) 1998 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
+#
+#	Can be freely distributed and used under the terms of the GNU GPL.
+#
+
+# Simple iterator
+m4_define(CF_itera, `m4_ifelse($#, 1, [[CF_iter($1)]], [[CF_iter($1)[[]]CF_itera(m4_shift($@))]])')
+m4_define(CF_iterate, `m4_define([[CF_iter]], m4_defn([[$1]]))CF_itera($2)')
+
+# Keywords are translated to C initializers
+m4_define(CF_handle_kw, `m4_divert(0){ "m4_translit($1,[[A-Z]],[[a-z]])", $1 },
+m4_divert(-1)')
+m4_define(CF_keywd, `m4_ifdef([[CF_tok_$1]],,[[m4_define([[CF_tok_$1]],1)CF_handle_kw($1)]])')
+m4_define(CF_KEYWORDS, `m4_define([[CF_toks]],[[]])CF_iterate([[CF_keywd]], [[$@]])m4_ifelse(CF_toks,,,%token[[]]CF_toks
+)DNL')
+
+# As we are processing C source, we must access all M4 primitives via
+# m4_* and also set different quoting convention: `[[' and ']]'
+m4_changequote([[,]])