boot update file task

boot-update-file.clj

(ns myns.core
  {:boot/export-tasks true}
  (:require
    [boot.core :as core]
    [clojure.edn :as edn]
    [clojure.java.io :as io]))

(core/deftask update-file
  "Updates files whose path matches `match-files` with the value returned from `expr`.
  `expr` is a function that takes the parsed content of the file and returns the new
  content of the file. Optionally, you can specify `parse-fn`, a function that takes the
  `slurp`ed content of the file and returns the parsed version. By default `parse-fn`
  is set to `clojure.edn/read-string`."
  [m match-files MATCH #{regex} "The set of regexes that the paths must match"
   e expr VAL code "The function called to transform the content of the matched files"
   p parse-fn VAL code "The function called to parse the files matched."]
  (when-not (and match-files expr)
    (throw (Exception. "need match-files and expr to update files.")))
  (core/with-pre-wrap
    fileset
    (let [parse-fn (or parse-fn edn/read-string)
          matching-tmp-files (->> fileset core/input-files (core/by-re match-files))
          update-content (comp expr parse-fn slurp core/tmp-file)]
      (core/commit!
        (reduce (fn [fileset tmp-file]
                  (let [new-dir (core/tmp-dir!)]
                    (-> (io/file new-dir (:path tmp-file))
                        (spit (update-content tmp-file)))
                    (core/add-resource fileset new-dir))) fileset matching-tmp-files)))))

You should add (io/make-parents new-dir (:path tmp-file)) before line 27 to make it work with nested paths.