Check in a little toy that graphs history of words in the source.

tools/git/graph.sh

+#!/bin/bash
+# Copyright (c) 2010 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+about="Given a grep expression, creates a graph of occurrences of that
+expression in the recent history of the tree.
+
+Prerequisites: git and GNU R (apt-get install r-base).
+"
+
+set -e
+
+target="$1"
+
+if [ -z $target ]; then
+    echo "usage: $0 <grep-compatible expression>"
+    echo
+    echo "$about"
+    exit 1
+fi
+
+datafile=$(mktemp)
+echo 'ago count' > $datafile
+for ago in $(seq 90 -1 0); do

[Nico, 2010/08/05 18:11:53]

`for ago in {90..0}; do` instead?

+    commit=$(git rev-list -1 --until="$ago days ago" origin/trunk)
+    git checkout -q -f $commit
+    count=$(git grep -E "$target" -- '*.cc' '*.h' '*.m' '*.mm' | wc -l)
+    echo "-$ago $count" >> $datafile
+    echo -n '.'
+done
+
+R CMD BATCH <(cat <<EOF

[Nico, 2010/08/05 18:11:53]

Neat, I wasn't actively aware that <() evaluates to a filename.

+data = read.delim("$datafile", sep=' ')
+png(width=600, height=300)
+plot(count ~ ago, type="l", main="$target", xlab='days ago', data=data)
+EOF
+) /dev/null
+
+echo done.
+
+rm -f $datafile

[Nico, 2010/08/05 18:11:53]

do you want a trap for this? if not, maybe a comment that says "this is simple
enough that we don't bother with a trap for clean up"?