I think shexp might deserve another look. It’s not an interpreter for a sexp-based shell language, as its name might unfortunately deceivingly suggest. It’s really a DSL for constructing shell pipelines using a 'a Process.t monad. The s-expression part is advertising that you can debug and trace the actions performed using s-expressions.
I’ve found Base plus Re to be sufficient for most of my string-manipulation needs. It’s never going to be as concise as Perl’s built-in “magic” support for regexps, but you gain explicitness and clarity, which is part of the benefit of OCaml anyway.