* (filename-resolve-user filename)
  resolves ~ and ~user in string filename

* (filename-resolve-variables filename)
  resolves variables in string filename

Please comment!

I used the LGPL v2 or later to add the option to include into Guile
later on. I would like to hear your opinions on that.
---
 src/Makefile.am      |  1 +
 src/string/posix.scm | 79 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 80 insertions(+)
 create mode 100644 src/string/posix.scm

diff --git a/src/Makefile.am b/src/Makefile.am
index 889a575..0425bd8 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -93,6 +93,7 @@ SOURCES = \
 	scheme/kwargs.scm		\
 	search/basic.scm		\
 	string/completion.scm		\
+	string/posix.scm		\
 	string/soundex.scm		\
 	string/transform.scm		\
 	string/wrap.scm			\
diff --git a/src/string/posix.scm b/src/string/posix.scm
new file mode 100644
index 0000000..5370657
--- /dev/null
+++ b/src/string/posix.scm
@@ -0,0 +1,79 @@
+;;; (string posix) -- posix string operations
+
+;; Copyright (C) 2020 Dr. Arne Babenhauserheide <arne_bab@web.de> and Leo Prikler
+
+;; This library is free software; you can redistribute it and/or
+;; modify it under the terms of the GNU Lesser General Public
+;; License as published by the Free Software Foundation; either
+;; version 2 of the License, or (at your option) any later version.
+
+;; This library 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
+;; Lesser General Public License for more details.
+
+;; You should have received a copy of the GNU Lesser General Public
+;; License along with this library. If not, see
+;; <http://www.gnu.org/licenses/>.
+#!
+;;; Commentary:
+Resolving ~ in filenames following POSIX rules.
+;;; Code:
+!#
+
+(define-module (string posix)
+  #:export (filename-resolve-user filename-resolve-variables)
+  #:use-module (ice-9 regex))
+
+(define (filename-resolve-user filename)
+  "Replaces ~ and ~user in string FILENAME as by posix rules.
+
+@lisp
+ (filename-resolve-user \"~\")
+=> (getenv \"HOME\") or /home/user or ~
+ (filename-resolve-user \"~other\")
+=> \"/home/other\" (or whatever dir entry other has in passwd
+@end lisp
+"
+  (cond
+   ((string= filename "~")
+    (or (getenv "HOME")
+        (passwd:dir (getpw (getlogin)))
+        "~"))
+   ((string-prefix? "~/" filename)
+    (string-replace filename
+                    (filename-resolve-user "~")
+                    0 1))
+   ((string-prefix? "~" filename)
+    (let ((matched (string-match "~([^/]*)" filename)))
+      (string-replace filename
+                      (passwd:dir (getpw (match:substring matched 1)))
+                      0 (match:end matched))))
+   (else filename)))
+
+(define (filename-resolve-variables filename)
+  "Resolve environment variables in string FILENAME
+
+@lisp
+ (filename-resolve-variables \"$HOME\")
+=> the home directory
+ (filename-resolve-user \"foo-$PWD-bar\")
+=> \"foo-thepwd-bar\" (with thepwd the working directory
+@end lisp
+
+"
+  (regexp-substitute/global #f "\\$([A-Za-z0-9_]+)" filename
+                            'pre
+                            (lambda (m)
+                              (or (getenv (match:substring m 1))
+                                  (error "Environment variable ~s not set"
+                                         (match:substring m 1))))
+                            'post))
+
+;; (define (test s)
+;;   (format #t "~a -> ~a~%" s (filename-resolve-user s)))
+;; 
+;; (test "~")
+;; (test "~/")
+;; (test "~gdm")
+;; (test "~gdm/")
-- 
2.28.0


-- 
Unpolitisch sein
heißt politisch sein
ohne es zu merken