+dnl awk-based implementation.
+dnl
+dnl The awk replacement currently has the following limitations:
+dnl
+dnl - Only the -v and -a options are supported.
+dnl
+dnl - Due to limitations of some awk implementations, a filename of "-"
+dnl to mean standard input should be avoided for the second file name.
+dnl Nevertheless, using "-" for the first filename should be portable.