Digging through Git History for Removed Text

July 31, 2022

1 min read

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git tool

Close up of a modern excavator bucket digging a hole in the ground by Ivan Radic is licensed under CC BY

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I aim to publish one article a month

Deleted files in Git

Git keeps a history of practically everything for your repository. I cannot state how powerful a tool it is, and has helped me immensely as I try to understand the why of some code.

There are times when I’ve tried to find something that doesn’t exist in the current revision but was in a previous version. I’ve always struggled with this, and I wanted a simpler and (hopefully) quicker way to conduct this search.

I decided to script my way to a solution that I feel happy about for now.

Let’s go Digging

This script ends up doing the following to search through Git history for matching text:

Search for any commits with any ‘additions/removals’ of the search query.
For each commit, get the list of files that contain the search query.
For each file, grep the git patch and print the lines that match the search query (with the match highlighted).

A lot of the git commands are leveraging the --pickaxe-regex -S<query> flags to search changes with regex powers:

-S<string>
  Look for differences that change the number of occurrences of the specified string (i.e. addition/deletion) in a file.

--pickaxe-regex
  Treat the <string> given to -S as an extended POSIX regular expression to match.

This would allow for the search query to leverage regular expressions. The following is an example of looking through my dotfiles repo for zgen (which is something I don’t use anymore).

❯ git dig "\szgen"
Searching for any commits with any 'additions/removals'
  Matching regex: "\szgen"

commit bd5dc58e9f94b7b62013a1378fbe7d101ccc70ec
Author: Kevin Jalbert <[email protected]>
Date:   Fri Jan 6 17:42:44 2017 -0500

    Update zsh.rake to install zplug instead of zgen

FILE -> tasks/zsh.rake
-  desc "Install zgen"
-    section "Installing zgen"

# Plus a few more commits

The git-dig Script

This GitHub Gist will be the canonical reference of the git-dig script (and will see updates as needed).

#!/usr/bin/env ruby

require 'optparse'
require 'open3'

def files_with_search_query(sha, search_query)
  `git show --format="" --name-only #{sha} -i --pickaxe-regex -S #{search_query}`.split("\n")
end

def grep_over_file(sha, file, search_query)
  git_show_cmd = "git show --format='' -p #{sha} -- '#{file}'"
  grep_cmd = "grep -i --color=always -E #{search_query}"
  `#{git_show_cmd} | #{grep_cmd}`
end

def git_pickaxe_search(search_query, options, &block)
  git_log_cmd = "git log --no-merges --format=%h"
  git_log_cmd += " --after=\"#{options[:after]}\"" if options[:after]
  git_log_cmd += " --before=\"#{options[:before]}\"" if options[:before]
  git_log_cmd += " -i --pickaxe-regex -S #{search_query}"

  Open3.popen3(git_log_cmd) do |stdin, stdout, stderr, thread|
    yield(stdout)
  end
end

def git_commit_info(sha)
  `git show --no-patch #{sha}`
end

def find_root_dir
  current_dir = Dir.pwd

  until Dir.exist?([current_dir, ".git"].join(File::SEPARATOR)) do
    parent_dir = File.dirname(current_dir)

    if parent_dir == current_dir
      puts "No .git repo found in path (or parent paths)."
      exit
    end

    current_dir = parent_dir
  end

  current_dir
end

# Handle options
options = {}
OptionParser.new do |opts|
  opts.banner = "Usage: git-dig [options] [regex query]"

  opts.on("--after=DATE", "Only searches commits more recent than the specific date.") do |v|
    options[:after] = v
  end

  opts.on("--before=DATE", "Only searches commits older recent than the specific date.") do |v|
    options[:before] = v
  end

  opts.on("-h", "--help", "Prints this help") do
    puts opts
    exit
  end
end.parse!

# Get search query
search_query = "\"#{ARGV.first}\""
if search_query == '""' # empty search as it would just be a pair of quotes
  puts "You need to pass a search term as input."
  exit
end

puts "Searching for any commits with any 'additions/removals'"
puts "  Matching regex: #{search_query}"
if options[:after] || options[:before]
  puts "  With search options: #{options}"
end
puts ""

# Get SHAs of all commits which had some 'addition/removal' of the search term
git_pickaxe_search(search_query, options) do |stdout|
  while line = stdout.gets
    exit if line.nil?

    sha = line.strip

    puts git_commit_info(sha)
    puts ""

    # Print diff of files which have search term
    files_with_search_query(sha, search_query).each do |file|
      puts "FILE -> #{file}"
      puts grep_over_file(sha, file, search_query)
      puts ""
    end

    puts "-"*80
    puts ""
  end
end

Alternative Solutions

To note, most Git GUIs have some search functionality in place which can satisfy the majority of this. Using the Git CLI is still a nice thing to be able to leverage though, which is why I went this route.