diff --git a/Documentation/default.1.do b/Documentation/default.1.do
index 26594b8..1d66fb4 100644
--- a/Documentation/default.1.do
+++ b/Documentation/default.1.do
@@ -1,2 +1,2 @@
-redo-ifchange md-to-man $1.md
+redo-ifchange md-to-man $1.md.tmp
 . ./md-to-man $1 $2 $3
diff --git a/Documentation/default.md.tmp.do b/Documentation/default.md.tmp.do
new file mode 100644
index 0000000..cc0ca4b
--- /dev/null
+++ b/Documentation/default.md.tmp.do
@@ -0,0 +1,3 @@
+redo-ifchange ../version/vars $1.md
+. ../version/vars
+sed -e "s/%VERSION%/$TAG/" -e "s/%DATE%/$DATE/" $1.md
diff --git a/Documentation/md-to-man.do b/Documentation/md-to-man.do
index 4ae53e7..d678313 100644
--- a/Documentation/md-to-man.do
+++ b/Documentation/md-to-man.do
@@ -1,5 +1,5 @@
 if pandoc </dev/null 2>/dev/null; then
-	echo 'pandoc -s -r markdown -w man -o $3 $1.md'
+	echo 'pandoc -s -r markdown -w man -o $3 $1.md.tmp'
 else
 	(IFS=:; for DIR in $PATH; do redo-ifcreate "$DIR/pandoc"; done)
 	echo "Warning: pandoc not installed; can't generate manpages." >&2
diff --git a/Documentation/redo-always.md b/Documentation/redo-always.md
index 47e13cc..a48da69 100644
--- a/Documentation/redo-always.md
+++ b/Documentation/redo-always.md
@@ -1,6 +1,6 @@
-% redo-always(1) Redo 0.00
+% redo-always(1) Redo %VERSION%
 % Avery Pennarun <apenwarr@gmail.com>
-% 2010-12-12
+% %DATE%
 
 # NAME
 
diff --git a/Documentation/redo-ifchange.md b/Documentation/redo-ifchange.md
index 7c4a71f..9405d73 100644
--- a/Documentation/redo-ifchange.md
+++ b/Documentation/redo-ifchange.md
@@ -1,6 +1,6 @@
-% redo-ifchange(1) Redo 0.00
+% redo-ifchange(1) Redo %VERSION%
 % Avery Pennarun <apenwarr@gmail.com>
-% 2010-12-12
+% %DATE%
 
 # NAME
 
diff --git a/Documentation/redo-ifcreate.md b/Documentation/redo-ifcreate.md
index 4a91672..12afd16 100644
--- a/Documentation/redo-ifcreate.md
+++ b/Documentation/redo-ifcreate.md
@@ -1,6 +1,6 @@
-% redo-ifcreate(1) Redo 0.00
+% redo-ifcreate(1) Redo %VERSION%
 % Avery Pennarun <apenwarr@gmail.com>
-% 2010-12-12
+% %DATE%
 
 # NAME
 
diff --git a/Documentation/redo-ood.md b/Documentation/redo-ood.md
index 3719920..823f651 100644
--- a/Documentation/redo-ood.md
+++ b/Documentation/redo-ood.md
@@ -1,6 +1,6 @@
-% redo-ood(1) Redo 0.00
+% redo-ood(1) Redo %VERSION%
 % Avery Pennarun <apenwarr@gmail.com>
-% 2010-12-19
+% %DATE%
 
 # NAME
 
diff --git a/Documentation/redo-sources.md b/Documentation/redo-sources.md
index 1023ea6..d6c3fe4 100644
--- a/Documentation/redo-sources.md
+++ b/Documentation/redo-sources.md
@@ -1,6 +1,6 @@
-% redo-sources(1) Redo 0.00
+% redo-sources(1) Redo %VERSION%
 % Avery Pennarun <apenwarr@gmail.com>
-% 2010-12-19
+% %DATE%
 
 # NAME
 
diff --git a/Documentation/redo-stamp.md b/Documentation/redo-stamp.md
index c965ad7..2cf7bc8 100644
--- a/Documentation/redo-stamp.md
+++ b/Documentation/redo-stamp.md
@@ -1,6 +1,6 @@
-% redo-stamp(1) Redo 0.00
+% redo-stamp(1) Redo %VERSION%
 % Avery Pennarun <apenwarr@gmail.com>
-% 2010-12-12
+% %DATE%
 
 # NAME
 
diff --git a/Documentation/redo-targets.md b/Documentation/redo-targets.md
index 4892a5a..e1af075 100644
--- a/Documentation/redo-targets.md
+++ b/Documentation/redo-targets.md
@@ -1,6 +1,6 @@
-% redo-targets(1) Redo 0.00
+% redo-targets(1) Redo %VERSION%
 % Avery Pennarun <apenwarr@gmail.com>
-% 2010-12-19
+% %DATE%
 
 # NAME
 
diff --git a/Documentation/redo.md b/Documentation/redo.md
index 2cbf201..2250249 100644
--- a/Documentation/redo.md
+++ b/Documentation/redo.md
@@ -1,6 +1,6 @@
-% redo(1) Redo 0.00
+% redo(1) Redo %VERSION%
 % Avery Pennarun <apenwarr@gmail.com>
-% 2010-12-12
+% %DATE%
 
 # NAME
 
diff --git a/_all.do b/_all.do
index 6623acb..f1d9513 100644
--- a/_all.do
+++ b/_all.do
@@ -1,2 +1,2 @@
 redo-ifchange redo-sh
-redo-ifchange Documentation/all
+redo-ifchange version/all Documentation/all
diff --git a/clean.do b/clean.do
index 938703b..16df2c3 100644
--- a/clean.do
+++ b/clean.do
@@ -5,6 +5,6 @@ if [ -e .do_built ]; then
 	done <.do_built
 fi
 [ -z "$DO_BUILT" ] && rm -rf .do_built .do_built.dir
-redo t/clean Documentation/clean
+redo t/clean Documentation/clean version/clean
 rm -f *~ .*~ */*~ */.*~ *.pyc install.wrapper
 find . -name '*.tmp' -exec rm -fv {} \;
diff --git a/version/.gitattributes b/version/.gitattributes
new file mode 100644
index 0000000..1dbc5f8
--- /dev/null
+++ b/version/.gitattributes
@@ -0,0 +1 @@
+gitvars.pre  export-subst
diff --git a/version/.gitignore b/version/.gitignore
new file mode 100644
index 0000000..dccdd45
--- /dev/null
+++ b/version/.gitignore
@@ -0,0 +1,3 @@
+/vars
+/gitvars
+/_version.py
diff --git a/version/__init__.py b/version/__init__.py
new file mode 100644
index 0000000..2863a1d
--- /dev/null
+++ b/version/__init__.py
@@ -0,0 +1 @@
+from _version import COMMIT, TAG, DATE
diff --git a/version/_version.py.do b/version/_version.py.do
new file mode 100644
index 0000000..cc22aad
--- /dev/null
+++ b/version/_version.py.do
@@ -0,0 +1,3 @@
+redo-ifchange vars
+cat vars
+
diff --git a/version/all.do b/version/all.do
new file mode 100644
index 0000000..db6567c
--- /dev/null
+++ b/version/all.do
@@ -0,0 +1,2 @@
+redo-ifchange vars _version.py
+
diff --git a/version/clean.do b/version/clean.do
new file mode 100644
index 0000000..16f3859
--- /dev/null
+++ b/version/clean.do
@@ -0,0 +1,3 @@
+rm -f *~ .*~ *.pyc _version.py vars gitvars
+
+
diff --git a/version/gitvars.do b/version/gitvars.do
new file mode 100644
index 0000000..0f2e698
--- /dev/null
+++ b/version/gitvars.do
@@ -0,0 +1,24 @@
+redo-ifchange gitvars.pre prodname
+
+read PROD <prodname
+
+# Fix each line from gitvars.pre where git may or may not have already
+# substituted the variables.  If someone generated a tarball with 'git archive',
+# then the data will have been substituted already.  If we're in a checkout of
+# the git repo, then it won't, but we can just ask git to do the substitutions
+# right now.
+while read line; do
+	# Lines *may* be of the form: $Format: ... $
+	x=${line#\$Format:}  # remove prefix
+	if [ "$x" != "$line" ]; then
+		# git didn't substitute it
+		x=${x%\$}  # remove trailing $
+		if [ "$x" == "%d" ]; then
+			tag=$(git describe --match="$PROD-*")
+			x="(tag: $tag)"
+		else
+			x=$(git log -1 --pretty=format:"$x")
+		fi
+	fi
+	echo "$x"
+done <gitvars.pre
diff --git a/version/gitvars.pre b/version/gitvars.pre
new file mode 100644
index 0000000..dc1efe4
--- /dev/null
+++ b/version/gitvars.pre
@@ -0,0 +1,3 @@
+$Format:%H$
+$Format:%d$
+$Format:%ci$
diff --git a/version/prodname b/version/prodname
new file mode 100644
index 0000000..f49789c
--- /dev/null
+++ b/version/prodname
@@ -0,0 +1 @@
+redo
diff --git a/version/vars.do b/version/vars.do
new file mode 100644
index 0000000..0da7597
--- /dev/null
+++ b/version/vars.do
@@ -0,0 +1,40 @@
+redo-ifchange gitvars prodname
+
+read PROD <prodname
+
+exec <gitvars
+read COMMIT
+read NAMES
+read DATE
+
+# the list of names is of the form:
+#   (x,y,tag: $PROD-####,tag: $PROD-####,a,b)
+# The entries we want are the ones starting with "tag: $PROD-" since those
+# refer to the right actual git tags.
+names_to_tag()
+{
+	x=${1#\(}
+	x=${x%\)}
+	cur=
+	while [ "$cur" != "$x" ]; do
+		cur=${x%%,*}
+		cur=${cur#tag: }
+		cur=${cur## }
+		tagpost=${cur#$PROD-}
+		if [ "$cur" != "$tagpost" ]; then
+			echo "$tagpost"
+			return 0
+		fi
+		x=${x#*,}
+	done
+	commitpost=${COMMIT#???????}
+	commitpre=${COMMIT%$commitpost}
+	echo "unknown-$commitpre"
+}
+
+
+sTAG=$(names_to_tag "$NAMES")
+
+echo "COMMIT='$COMMIT'"
+echo "TAG='$sTAG'"
+echo "DATE='${DATE%% *}'"