new file mode 100644
--- /dev/null
+++ b/lib/concat-filename.c
@@ -0,0 +1,70 @@
+/* Construct a full pathname from a directory and a filename.
+   Copyright (C) 2001-2004, 2006, 2007 Free Software Foundation, Inc.
+
+   This program 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 2, or (at your option) any
+   later version.
+
+   This program 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, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
+   USA.  */
+
+/* Written by Bruno Haible <haible@clisp.cons.org>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include "pathname.h"
+
+#include <string.h>
+
+#include "xalloc.h"
+
+/* Concatenate a directory pathname, a relative pathname and an optional
+   suffix.  The directory may end with the directory separator.  The second
+   argument may not start with the directory separator (it is relative).
+   Return a freshly allocated pathname.  */
+char *
+concatenated_pathname (const char *directory, const char *filename,
+		       const char *suffix)
+{
+  char *result;
+  char *p;
+
+  if (strcmp (directory, ".") == 0)
+    {
+      /* No need to prepend the directory.  */
+      result = XNMALLOC (strlen (filename)
+			 + (suffix != NULL ? strlen (suffix) : 0)
+			 + 1,
+			 char);
+      p = result;
+    }
+  else
+    {
+      size_t directory_len = strlen (directory);
+      int need_slash =
+	(directory_len > FILE_SYSTEM_PREFIX_LEN (directory)
+	 && !ISSLASH (directory[directory_len - 1]));
+      result = XNMALLOC (directory_len + need_slash
+			 + strlen (filename)
+			 + (suffix != NULL ? strlen (suffix) : 0)
+			 + 1,
+			 char);
+      memcpy (result, directory, directory_len);
+      p = result + directory_len;
+      if (need_slash)
+	*p++ = '/';
+    }
+  p = stpcpy (p, filename);
+  if (suffix != NULL)
+    stpcpy (p, suffix);
+  return result;
+}