If you get this, when trying to install apache2 (port install apache2), on Leopard.

Undefined symbols:
  "_ap_ugly_hack", referenced from:
      _ap_ugly_hack$non_lazy_ptr in libmain.a(main.o)
  "_ap_prelinked_module_symbols", referenced from:
      _ap_prelinked_module_symbols$non_lazy_ptr in libmain.a(core.o)
  "_ap_prelinked_modules", referenced from:
      _ap_prelinked_modules$non_lazy_ptr in libmain.a(main.o)
      _ap_prelinked_modules$non_lazy_ptr in libmain.a(config.o)
  "_ap_http_input_filter_handle", referenced from:
      _ap_http_input_filter_handle$non_lazy_ptr in libmain.a(protocol.o)
  "_ap_preloaded_modules", referenced from:
      _ap_preloaded_modules$non_lazy_ptr in libmain.a(config.o)

Simply install gawk port install gawk, then port clean apache2, and port install apache2.

Don't know really why, maybe the awk in Tiger was a GNU awk, and it has changed in Leopard ...

I've opened a ticket on macforge #13066