[Feature] sub()/gsub() can replace the empty regex [POSIX awk] unknown? [GNU awk 3.1.6] yes [Busybox awk 1.11.3] yes [mawk 1.3.3] yes [nawk (solaris 2.8)] only with o* (see sample code) yes [tawk x.xx] unknown yes [NetBSD? awk 20030729] yes, but only with an implicit regex (see sample code) [jawk 1.02] 
yes