---
title: Code Sleuthing with Git
teaser: Git can help you uncover the history of a code snippet.
tags: git
author: Ian C. Anderson
published_on: 2015-03-31
---

Let's say you want to delete a method `foo` that seems to be dead code.
You use a tool like `grep` to find callers of `foo`, and there are no results.
It's tempting to consider `foo` to be unused at this point, but you
want to know the story of this method so you can be confident in removing it.
Why did this method ever exist?

## Search your commits

From the [git-log](http://git-scm.com/docs/git-log) docs:

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

Git will spit out all of the commits that either deleted or added the given
string (e.g. calls to a method). Unlike `git log --grep`, `git log -S` actually
searches the _code_ in the repo, not the commit messages.

```documentation
$ git log -S foo

    commit 8f19a1fa0...
    Author: Ian C. Anderson
    Date:   Fri Mar 27 21:44:17 2015 -0500

        stop using the foo method because eww

    commit 216895189...
    Author: Ian C. Anderson
    Date:   Thu Mar 6 21:09:44 1999 -0500

        new foo method - so great!
```

## Search your commits by regex

```documentation
-G <regex>
    Look for differences whose patch text contains added/removed lines that match <regex>.
```

This `-G` option becomes handy when you're looking for a pattern instead of a
literal string.

Consider a `bar` method that has 1 argument with a default value, but
none of the current calls to `bar` use the default value. Let's use `-G` to
look for past usages of `bar` that _did_ use the default value (by looking
for the string `bar` without a following parenthesis).

```documentation
$ git log -G "bar[^(]"

    commit 8f19a1fa1...
    Author: Ian C. Anderson
    Date:   Fri Mar 27 21:44:17 2015 -0500

        remove custom args to bar method

    commit 216895180...
    Author: Ian C. Anderson
    Date:   Thu Mar 6 21:09:44 1999 -0500

        new bar method
```

We now see all of the commits that added or removed a line matching our pattern.

These two commands have become indispensable tools for me, especially when
navigating and refactoring large and/or legacy codebases.

For a thorough guide to practical Git techniques, check out thoughtbot's
[_Goal-Oriented Git_](http://goal-oriented-git.com) book, written by developer
[George Brocklehurst](https://twitter.com/georgebrock).

For a convenient and productive way to run git commands in the terminal, give
[gitsh](https://github.com/thoughtbot/gitsh) a try.