#!/bin/sh
# Substitute CONFIG_ variables
awk '
    function subst(force)
    {
	if (!done || force) {
	    if (has_value)
		print symbol "=" value
	    else
		print "# " symbol " is not set"
	}
	done=1
    }

    BEGIN           { symbol = ARGV[1]
		     if (ARGC == 3) {
			 has_value=1
			 value = ARGV[2]
		     }
		     split("", ARGV)
		    }
    match($0, "\\<" symbol "\\>") \
		    { subst(1) ; next }
		    { print }
    END             { subst(0) }
' "$@"