sed -i -E "s/еж([аиу][^а-я])/ёжик\1/g" *ru*
grep -E "еж[аиу][^а-я]" *ru*
Comment: [^а-я] includes all spaces and punctuation and also finish of string
AAAB1nicJY5HjsUwDEPpnjq5sAP44BIy5NfmgWoUxztelLe8wNuliG1i4pp14plJioAnX5lAdjhKgGULsNED1TECw/H55+shaFBlUGXQVfbo0YWDJtXUK4Gq2+IryTQ5n9ZA0R50kfTtB5ZDgTpXqLJ+8LZEoOarK0tSlqS9KlWl/qzZughc1g1ngOUeKIYtkA0j8BkeG7Y+ggZZBlkGUIno0YWDXWpX7wxk3RZbt0xvq4YjULTXddH07QeWQ4E2rlBV/eDtGYGSrU1ZbmW5tXdIHVL/NLTKIw==