Spacemacs project search replace

spacemacs-project-search-replace

SPC s f (helm-files-smart-do-search) - this will bring up HELM File Completions
navigate to the directory from which to do the search - use C-h to go up one level if needs be
type the search string
hit C-c C-e (helm-ag-edit)

Once in helm-ag-edit edit as in a normal buffer
For example :%s/foo/bar/g
hit C-c C-c to save

For case-sensitive/insensitive toggle by
spc spc (HELM M-x)
toggle-case-fold-search
then search with /foo
and replace with :%s//bar/g