--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2009-03-01  Bruno Haible  <bruno@clisp.org>
+
+	* gnulib-tool (sed): Do alias as "sed --posix" if sed's version is at
+	least 4.2.
+
 2009-03-01  Eric Blake  <ebb9@byu.net>
             Bruno Haible  <bruno@clisp.org>
 

--- a/gnulib-tool
+++ b/gnulib-tool
@@ -63,28 +63,32 @@
   AUTOPOINT="${GETTEXTPATH}autopoint"
 fi
 
-# Disabled because "sed --posix" is buggy in GNU sed 4.1.5, see
+# When using GNU sed, turn off as many GNU extensions as possible,
+# to minimize the risk of accidentally using non-portable features.
+# However, do this only for gnulib-tool itself, not for the code that
+# gnulib-tool generates, since we don't want "sed --posix" to leak
+# into makefiles. And do it only for sed versions 4.2 or newer,
+# because "sed --posix" is buggy in GNU sed 4.1.5, see
 # <http://lists.gnu.org/archive/html/bug-gnulib/2009-02/msg00225.html>.
-if false; then
-  # When using GNU sed, turn off as many GNU extensions as possible,
-  # to minimize the risk of accidentally using non-portable features.
-  # However, do this only for gnulib-tool itself, not for the code that
-  # gnulib-tool generates, since we don't want "sed --posix" to leak
-  # into makefiles.
-  if (alias) > /dev/null 2>&1 && echo | sed --posix -e d >/dev/null 2>&1; then
-    # Define sed as an alias.
-    # It is not always possible to use aliases. Aliases are guaranteed to work
-    # if the executing shell is bash and either it is invoked as /bin/sh or
-    # is a version >= 2.0, supporting shopt. This is the common case.
-    # Two other approaches (use of a variable $sed or of a function func_sed
-    # instead of an alias) require massive, fragile code changes.
-    # An other approach (use of function sed) requires `which sed` - but
-    # 'which' is hard to emulate, due to missing "test -x" on some platforms.
-    if test -n "$BASH_VERSION"; then
-      shopt -s expand_aliases >/dev/null 2>&1
-    fi
-    alias sed='sed --posix'
+if (alias) > /dev/null 2>&1 \
+   && echo | sed --posix -e d >/dev/null 2>&1 \
+   && case `sed --version | sed -e 's/^[^0-9]*//' -e 1q` in \
+        [1-3]* | 4.[01]*) false;; \
+        *) true;; \
+      esac \
+   ; then
+  # Define sed as an alias.
+  # It is not always possible to use aliases. Aliases are guaranteed to work
+  # if the executing shell is bash and either it is invoked as /bin/sh or
+  # is a version >= 2.0, supporting shopt. This is the common case.
+  # Two other approaches (use of a variable $sed or of a function func_sed
+  # instead of an alias) require massive, fragile code changes.
+  # An other approach (use of function sed) requires `which sed` - but
+  # 'which' is hard to emulate, due to missing "test -x" on some platforms.
+  if test -n "$BASH_VERSION"; then
+    shopt -s expand_aliases >/dev/null 2>&1
   fi
+  alias sed='sed --posix'
 fi
 
 # sed_noop is a sed expression that does nothing.