Add git-spacehogs script

The git-spacehogs script can be used on a cloned repository to go
through your git history and locate large commits / files and will
prompt you to remove them.

git-spacehogs

+#!/bin/bash
+
+################################################################################
+################################################################################
+# DISCLAIMER:
+
+# It is recommended that you clone your project somewhere safe as a backup; e.g.
+# 'git clone https://git_url/group/project.git ~/projects/project-backup'
+
+# This script _WILL_ perform destructive changes on a repository
+################################################################################
+################################################################################
+# INFOS:
+
+# If 'git remote' displays any remotes, the 'true' size (after running this
+# script) of the repository will not be 'seen' with 'du -sh'; remove remotes
+# or force push your updated project to see the new reduced size.
+
+# To push updated / cleaned history to the remote, you will need to execute
+# a 'force' push; e.g. 'git push -f <remote_name> <branch>'; some services
+# like GitLab protect branches and will prevent a force push, without removing
+# protection from the branch in question.
+
+# To remove protection from a branch (and re-add it) browse to:
+# https://<gitlab_url>/<namespace>/<project>/protected_branches or
+# Click the gear in the upper right and click "Protected Branches"
+################################################################################
+################################################################################
+
+# Additional info
+# https://git-scm.com/book/en/v2/Git-Internals-Maintenance-and-Data-Recovery
+# http://stackoverflow.com/questions/3765234/listing-and-deleting-git-commits-that-are-under-no-branch-dangling
+
+# find the git directory for the repository we are in
+git_dir="$(git rev-parse --show-toplevel)/.git"
+
+# default to the 10 largest blobs
+number=5
+if [[ "$1" =~ [0-9] ]]; then
+  number=$1
+fi
+
+process_blob() {
+  blob="$1"
+
+  # Get files included in the blob
+  files=$(git rev-list --objects --all | grep "$blob" | awk '{print $2}')
+  for file in $files; do
+    printf "%s\n" "$file"
+    read -p "Remove? [y/N] " confirm
+    if [ "$confirm" == 'Y' ] || [ "$confirm" == 'y' ]; then
+      # Find the first commit the file appears in
+      first=$(git log --oneline --branches -- $file \
+              | tail -n1 \
+              | awk '{print $1}')
+      if [[ -z "$first" ]]; then
+        printf "Can't find commit for %s; has it been removed already?\n" 1>&2
+      else
+        # Remove the file from the commit and rewrite history
+        # More info:
+        git filter-branch -f --index-filter \
+          "git rm --ignore-unmatch --cached "$file"" -- "$first"^..
+      fi
+    fi
+  done
+}
+
+# Run git's garbage collection
+git gc
+
+# Get all git objects, including  size on disk, filter out junk
+objects=$(git verify-pack -v $git_dir/objects/pack/pack-*.idx \
+  | grep blob \
+  | sort -rk3 -n \
+  | head -n $number)
+
+# Open FD 3 to read the contents of "$objects"
+# (Necessary to use 'read' / STDIN elsewhere)
+exec 3<<<"$objects"
+
+while read -u 3 -rd $'\n' object; do
+  awk '{printf "%s %0.2fM\n", $1, $3/1024/1024}' <<< "$object"
+  process_blob $(echo "$object" | awk '{print $1}')
+done
+
+# Close FD 3
+exec 3<&-
+
+# Ensure "$git_dir" is set so we don't try 'rm -rf /refs/original' or something
+if [[ -n "$git_dir" ]]; then
+  rm -rf "$git_dir"/refs/original
+  rm -rf "$git_dir"/logs/
+  git fsck --full
+  git reflog expire --expire-unreachable=now --all
+  git gc --prune=now
+fi