zshhasoptions
Re:OpenBSD will shut down if we do not have the funding to keep the li...
on Thursday January 16, 2014 @06:27PM (#7073205)
try adding setopt HIST_SAVE_NO_DUPS to your .zshrc
you could also have a look at HIST_FIND_NO_DUPS and HIST_IGNORE_ALL_DUPS (more options at http://zsh.sourceforge.net/Doc/Release/Options.html )
If you still use bash, now is a good time to upgrade to zsh