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diff --git a/src/data/util.lisp b/src/data/util.lisp
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+;;; Consfigurator -- Lisp declarative configuration management system
+
+;;; Copyright (C) 2022  David Bremner <david@tethera.net>
+
+;;; This file is free software; you can redistribute it and/or modify
+;;; it under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3, or (at your option)
+;;; any later version.
+
+;;; This file is distributed in the hope that it will be useful,
+;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+
+;;; You should have received a copy of the GNU General Public License
+;;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+(in-package :consfigurator.data.util)
+(named-readtables:in-readtable :consfigurator)
+
+(defun literal-data-pathname (base-path iden1 iden2 &key type)
+  "Generate a path from BASE-PATH, IDEN1 and IDEN2 by concatentation,
+optionally adding extension TYPE.
+
+No escaping of special characters is done, but extra '/' characters between
+pathname components are removed.
+
+The intended use case is to map IDEN1 and IDEN2 to files in a user-maintained
+hierarchy under BASE-PATH.  In particular IDEN2 and (if prefixed by '_') IDEN1
+may contain '/' characters to map into multiple levels of directory."
+  (let ((base-dir (uiop:parse-unix-namestring base-path :ensure-directory t)))
+    (unless (uiop:directory-pathname-p base-dir)
+      (simple-program-error "~A does not specify a directory" base-dir))
+    (merge-pathnames
+     (uiop:relativize-pathname-directory
+      (uiop:parse-unix-namestring iden2 :type type))
+     (merge-pathnames
+      (uiop:relativize-pathname-directory
+       (ensure-directory-pathname iden1))
+      base-dir))))