diff --git a/README.md b/README.md
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+# git-heatmap
+
+> Display a heatmap for oft-edited files
+
+![screenshot of git heatmap](screenshot.png)
+
+## Install
+
+### Dependencies
+
+You must have the `bars` command on your system first:
+
+```
+npm install -g https://github.com/jez/bars.git
+```
+
+### Installation
+
+Download `git-heatmap` and put it on your path.
+
+```bash
+# Homebrew:
+brew install jez/formulae/git-heatmap
+```
+
+## Usage
+
+```
+❯ git heatmap -h
+Heatmap of oft-edited files.
+
+Usage:
+  git heatmap [options] [<path>...]
+
+Options:
+  -n <top>                      Limit to top <n> files. [default: 30]
+  --width <n>                   Limit histogram to <n> chars.
+  -b <branch>, --base <branch>  Compare relative to <branch>. If on <branch>,
+                                show heatmap for entire repo. [default: master]
+  -h                            Show this message.
+```
+
+## License
+
+[![MIT License](https://img.shields.io/badge/license-MIT-blue.svg)](https://jez.io/MIT-LICENSE.txt)
diff --git a/git-heatmap b/git-heatmap
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+#!/usr/bin/env bash
+
+# Build a commit frequency histogram
+
+ccyan="$(echo -ne '\033[0;36m')"
+cnone="$(echo -ne '\033[0m')"
+
+argv=()
+while [[ $# -gt 0 ]]; do
+  key="$1"
+  case $key in
+    -n)
+      LIMIT="$2"
+      shift
+      shift
+      ;;
+    -b|--base)
+      REVIEW_BASE="$2"
+      shift
+      shift
+      ;;
+    -h)
+      cat <<EOF
+Heatmap of oft-edited files.
+
+Usage:
+  git heatmap [options] [<path>...]
+
+Options:
+  -n <top>                      Limit to top <n> files. [default: 30]
+  -b <branch>, --base <branch>  Compare relative to <branch>. If on <branch>,
+                                show heatmap for entire repo. [default: master]
+  -h                            Show this message.
+EOF
+      exit
+      ;;
+    *)
+      argv+=("$1")
+      shift
+      ;;
+  esac
+done
+
+LIMIT=${LIMIT:-30}
+REVIEW_BASE=${REVIEW_BASE:-master}
+
+files() {
+  git log --name-status --pretty=format: -- "${argv[@]}" | cut -f 2-
+}
+
+color_name() {
+  # \(.*\/\)\([^/ ]*\)
+  sed -e "s/\(..*\/\)*\(.[^|]*\) |/\1$ccyan\2$cnone |/"
+}
+
+filter() {
+  sort | \
+    uniq -c | \
+    sort -nr | \
+    tail -n +2 | \
+    head -n "$LIMIT"
+}
+
+if [[ "$(git branch | grep '\*')" =~ $REVIEW_BASE ]]; then
+  # If on master, show heatmap for whole repo
+  files | filter | bars --bar █ | color_name
+else
+  MERGE_BASE="$(git merge-base HEAD "$REVIEW_BASE")"
+  files | \
+    # If on separate branch, show heatmap for files changed since master
+    grep -xF -f <(git diff --name-only "$MERGE_BASE") | \
+    filter | \
+    bars --bar █ | \
+    color_name
+fi
+
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