Zsh RVM requires : The use of globs that can possible be empty (no matches). If you experience glob problems try setting 'setopt nullglob' in your zsh profiles. Shell regex support via the operator =~. =~ appeared first in 4.3.5,(it was added in zsh-workers-23375. ) how can I tell if my version of zsh supports =~ ? $ foo=baaaar; [[ $foo =~ ba*r ]] && echo "Your shell supports the =~ regex operator