git-reference/inspect/index.html

---
layout: reference
---

<div class="box">
  <h2>
    <span class="docs">
      <a target="new" href="http://progit.org/book/ch2-3.html">book</a>
    </span>
    Inspection and Comparison
  </h2>
  <div class="block">
    <p>
    So now you have a bunch of branches that you are using for short lived
    topics, long lived features and what not.  How do you keep track of them?
    Git has a couple of tools to help you figure out where work was done, what
    the difference between two branches are and more.
    </p>

    <p class="nutshell">
    <b>In a nutshell</b> you can use <code>git log</code> to find specific
    commits in your project history - by author, date, content or
    history.  You can use <code>git diff</code> to compare two different points
    in your history - generally to see how two branches differ or what has
    changed from one version of your software to another.
    </p>
  </div>
</div>

<div class="box">
  <h2>
    <span class="docs">
      <a target="new" href="http://git-scm.com/docs/git-log">docs</a> &nbsp;
      <a target="new" href="http://progit.org/book/ch2-3.html">book</a>
    </span>
    <a name="log">git log</a>
    <span class="desc">filter your commit history</span>
  </h2>

  <div class="block">
    <p>We've already seen how to use <code>git log</code> to compare branches,
    by looking at the commits on one branch that are not reachable from another.
    (If you don't remember, it looks like this: <code>git log branchA ^branchB</code>).
    However, you can also use <code>git log</code> to look for specific commits.
    Here we'll be looking at some of the more commonly used <code>git log</code>
    options, but there are many.  Take a look at the official docs for the whole
    list.
    </p>

    <h4>
      git log --author
      <small>look for only commits from a specific author</small>
    </h4>

    <p>
    To filter your commit history to only the ones done by a specific author,
    you can use the <code>--author</code> option.  For example, let's say we're
    looking for the commits in the Git source code done by Linus.  We would
    type something like <code>git log --author=Linus</code>. The search is
    case sensitive and also will search the email address.  I'll do the
    example using the <code>-[number]</code> option, which will limit the
    results to the last [number] commits.
    </p>

<pre>
<b>$ git log --author=Linus --oneline -5</b>
81b50f3 Move 'builtin-*' into a 'builtin/' subdirectory
3bb7256 make "index-pack" a built-in
377d027 make "git pack-redundant" a built-in
b532581 make "git unpack-file" a built-in
112dd51 make "mktag" a built-in
</pre>

    <h4>
      git log --since --before
      <small>filter commits by date committed</small>
    </h4>

    <p>
    If you want to specify a date range that you're interested in filtering your
    commits down to, you can use a number of options - I use <code>--since</code>
    and <code>--before</code>, but you can also use <code>--until</code> and
    <code>--after</code>.  For example, if I wanted to see all the commits in
    the Git project before 3 weeks ago but after April 18th, I could run this
    (I'm also going to use <code>--no-merges</code> to remove merge commits):
    </p>

<pre>
<b>$ git log --oneline --before={3.weeks.ago} --after={2010-04-18} --no-merges</b>
5469e2d Git 1.7.1-rc2
d43427d Documentation/remote-helpers: Fix typos and improve language
272a36b Fixup: Second argument may be any arbitrary string
b6c8d2d Documentation/remote-helpers: Add invocation section
5ce4f4e Documentation/urls: Rewrite to accomodate transport::address
00b84e9 Documentation/remote-helpers: Rewrite description
03aa87e Documentation: Describe other situations where -z affects git diff
77bc694 rebase-interactive: silence warning when no commits rewritten
636db2c t3301: add tests to use --format="%N"
</pre>

    <h4>
      git log --grep
      <small>filter commits by commit message</small>
    </h4>

    <p>
      You may also want to look for commits with a certain phrase in the commit
      message.  You can use <code>--grep</code> for that.  Let's say I knew there
      was a commit that dealt with using the P4EDITOR environment variable and
      I wanted to remember what that change looked like - I could find the commit
      with <code>--grep</code>.
    </p>

<pre>
<b>$ git log --grep=P4EDITOR --no-merges</b>
<span class="yellow">commit 82cea9ffb1c4677155e3e2996d76542502611370</span>
Author: Shawn Bohrer
Date:   Wed Mar 12 19:03:24 2008 -0500

    git-p4: Use P4EDITOR environment variable when set

    Perforce allows you to set the P4EDITOR environment variable to your
    preferred editor for use in perforce.  Since we are displaying a
    perforce changelog to the user we should use it when it is defined.

    Signed-off-by: Shawn Bohrer <shawn.bohrer@gmail.com>
    Signed-off-by: Simon Hausmann <simon@lst.de>
</pre>

    <p>
    Git will logically OR all <code>--grep</code> and <code>--author</code>
    arguments.  If you want to use <code>--grep</code> and <code>--author</code>
    to see commits that were authored by someone AND have a specific message
    content, you have to add the <code>--all-match</code> option. In these
    examples, I'm going to use the <code>--format</code> option, so we can see
    who the author of each commit was.
    </p>

    <p>If I look for the commit messages with 'p4 depo' in them, I get these
    three commits:</p>

<pre>
<b>$ git log --grep="p4 depo" --format="%h %an %s"</b>
ee4fd1a Junio C Hamano Merge branch 'master' of git://repo.or.cz/git/fastimport
da4a660 Benjamin Sergeant git-p4 fails when cloning a p4 depo.
1cd5738 Simon Hausmann Make incremental imports easier to use by storing the p4 d
</pre>

    <p>If I add a <code>--author=Hausmann</code> argument, instead of further
    filtering it down to the one commit by Simon, it instead will show me all
    commits by Simon OR commits with "p4 depo" in the message:</p>

<pre>
<b>$ git log --grep="p4 depo" --format="%h %an %s" --author="Hausmann"</b>
cdc7e38 Simon Hausmann Make it possible to abort the submission of a change to Pe
f5f7e4a Simon Hausmann Clean up the git-p4 documentation
30b5940 Simon Hausmann git-p4: Fix import of changesets with file deletions
4c750c0 Simon Hausmann git-p4: git-p4 submit cleanups.
0e36f2d Simon Hausmann git-p4: Removed git-p4 submit --direct.
edae1e2 Simon Hausmann git-p4: Clean up git-p4 submit's log message handling.
4b61b5c Simon Hausmann git-p4: Remove --log-substitutions feature.
36ee4ee Simon Hausmann git-p4: Ensure the working directory and the index are cle
e96e400 Simon Hausmann git-p4: Fix submit user-interface.
38f9f5e Simon Hausmann git-p4: Fix direct import from perforce after fetching cha
2094714 Simon Hausmann git-p4: When skipping a patch as part of "git-p4 submit" m
1ca3d71 Simon Hausmann git-p4: Added support for automatically importing newly ap
...
</pre>

    <p>However, if I add a <code>--all-match</code>, I get the results I'm
    looking for:</p>

<pre>
<b>$ git log --grep="p4 depo" --format="%h %an %s" --author="Hausmann" --all-match</b>
1cd5738 Simon Hausmann Make incremental imports easier to use by storing the p4 d
</pre>

    <h4>
      git log -S
      <small>filter by introduced diff</small>
    </h4>

    <p>
      What if you write really horrible commit messages?  Or, what if you are
      looking for when a function was introduced, or where variables started
      to be used?  You can also tell Git to look through the diff of each
      commit for a string.  For example, if we wanted to find which commits
      modified anything that looked like the function name
      'userformat_find_requirements', we would run this: (note there is no '='
      between the '-S' and what you are searching for)
    </p>

<pre>
<b>$ git log -Suserformat_find_requirements</b>
<span class="yellow">commit 5b16360330822527eac1fa84131d185ff784c9fb</span>
Author: Johannes Gilger
Date:   Tue Apr 13 22:31:12 2010 +0200

    pretty: Initialize notes if %N is used

    When using git log --pretty='%N' without an explicit --show-notes, git
    would segfault. This patches fixes this behaviour by loading the needed
    notes datastructures if --pretty is used and the format contains %N.
    When --pretty='%N' is used together with --no-notes, %N won't be
    expanded.

    This is an extension to a proposed patch by Jeff King.

    Signed-off-by: Johannes Gilger
    Signed-off-by: Junio C Hamano
</pre>

    <h4>
      git log -p
      <small>show patch introduced at each commit</small>
    </h4>

    <p>
    Each commit is a snapshot of the project, but since each commit records the
    snapshot it was based off of, Git can always calculate the difference and
    show it to you as a patch.  That means for any commit you can get the patch
    that commit introduced to the project.  You can either do this by running
    <code>git show [SHA]</code> with a specific commit SHA, or you can run
    <code>git log -p</code>, which tells Git to put the patch after each commit.
    It is a great way to summarize what has happened on a branch or between
    commits.
    </p>

<pre>
<b>$ git log -p --no-merges -2</b>
<span class="yellow">commit 594f90bdee4faf063ad07a4a6f503fdead3ef606</span>
Author: Scott Chacon schacon@gmail.com
Date:   Fri Jun 4 15:46:55 2010 +0200

    reverted to old class name

<span class="umber">diff --git a/ruby.rb b/ruby.rb
index bb86f00..192151c 100644
--- a/ruby.rb
+++ b/ruby.rb</span>
<span class="lblue">@@ -1,7 +1,7 @@</span>
<span class="red">-class HiWorld</span>
<span class="green">+class HelloWorld</span>
   def self.hello
     puts "Hello World from Ruby"
   end
 end

<span class="red">-HiWorld.hello</span>
<span class="green">+HelloWorld.hello</span>

<span class="yellow">commit 3cbb6aae5c0cbd711c098e113ae436801371c95e</span>
Author: Scott Chacon schacon@gmail.com
Date:   Fri Jun 4 12:58:53 2010 +0200

    fixed readme title differently

<span class="umber">diff --git a/README b/README
index d053cc8..9103e27 100644
--- a/README
+++ b/README</span>
<span class="lblue">@@ -1,4 +1,4 @@</span>
<span class="red">-Hello World Examples</span>
<span class="green">+Many Hello World Examples</span>
 ======================

 This project has examples of hello world in
</pre>

    <p>This is a really nice way of summarizing changes or reviewing a series
    of commits before merging them or releasing something.</p>

    <h4>
      git log --stat
      <small>show diffstat of changes introduced at each commit</small>
    </h4>

    <p>If the <code>-p</code> option is too verbose for you, you can summarize
    the changes with <code>--stat</code> instead. Here is the same log output
    with <code>--stat</code> instead of <code>-p</code></p>

<pre>
<b>$ git log --stat --no-merges -2</b>
<span class="yellow">commit 594f90bdee4faf063ad07a4a6f503fdead3ef606</span>
Author: Scott Chacon schacon@gmail.com
Date:   Fri Jun 4 15:46:55 2010 +0200

    reverted to old class name

 ruby.rb |    4 <span class="green">++</span><span class="red">--</span>
 1 files changed, 2 insertions(+), 2 deletions(-)

<span class="yellow">commit 3cbb6aae5c0cbd711c098e113ae436801371c95e</span>
Author: Scott Chacon schacon@gmail.com
Date:   Fri Jun 4 12:58:53 2010 +0200

    fixed readme title differently

 README |    2 <span class="green">+</span><span class="red">-</span>
 1 files changed, 1 insertions(+), 1 deletions(-)
</pre>

    <p>Same basic information, but a little more compact - it still lets you
    see relative changes and which files were modified.</p>

  </div>
</div>

<div class="box">
  <h2>
    <span class="docs">
      <a target="new" href="http://git-scm.com/docs/git-diff">docs</a> &nbsp;
      <a target="new" href="http://progit.org/book/ch5-3.html#determining_what_is_introduced">book</a>
    </span>
    <a name="diff">git diff</a>
    <span class="desc"></span>
  </h2>

  <div class="block">

    <p>Finally, to see the absolute changes between any two commit snapshots,
    you can use the <code>git diff</code> command. This is largely used in two
    main situations - seeing how two branches differ from one another and
    seeing what has changed since a release or some other older point in
    history.  Let's look at both of these situations.</p>

    <p>To see what has changed since the last release, you can simply run
    <code>git diff [version]</code> (or whatever you tagged the release).
    For example, if we want to see what has changed in our project since
    the v0.9 release, we can run <code>git diff v0.9</code>.
    </p>

<pre>
<b>$ git diff v0.9</b>
<span class="umber">diff --git a/README b/README
index d053cc8..d4173d5 100644
--- a/README
+++ b/README</span>
<span class="lblue">@@ -1,4 +1,4 @@</span>
<span class="red">-Hello World Examples</span>
<span class="green">+Many Hello World Lang Examples</span>
 ======================

 This project has examples of hello world in
<span class="umber">diff --git a/ruby.rb b/ruby.rb
index bb86f00..192151c 100644
--- a/ruby.rb
+++ b/ruby.rb</span>
<span class="lblue">@@ -1,7 +1,7 @@</span>
<span class="red">-class HiWorld</span>
<span class="green">+class HelloWorld</span>
   def self.hello
     puts "Hello World from Ruby"
   end
 end

<span class="red">-HiWorld.hello</span>
<span class="green">+HelloWorld.hello</span>
</pre>

    <p>Just like <code>git log</code>, you can use the <code>--stat</code>
      option with it.</p>

<pre>
<b>$ git diff v0.9 --stat</b>
 README  |    2 +-
 ruby.rb |    4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)
</pre>

    <p>To compare two divergent branches, however, you can run something like
    <code>git diff branchA branchB</code> but the problem is that it will do
    exactly what you are asking - it will basically give you a patch file that
    would turn the snapshot at the tip of branchA into the snapshot at the tip
    of branchB.  This means if the two branches have diverged - gone in different
    directions - it will remove all the work that was introduced into branchA
    and then add everything that was introduced into branchB.  This is probably
    not what you want - you want the changes added to branchB that are not in
    branchA, so you really want the difference between where the two branches
    diverged and the tip of branchB. So, if our history looks like this:</p>

<pre>
<b>$ git log --graph --oneline --decorate --all</b>
* 594f90b (HEAD, tag: v1.0, master) reverted to old class name
| * 1834130 (erlang) added haskell
| * ab5ab4c added erlang
|/
*   8d585ea Merge branch 'fix_readme'
...
</pre>

    <p>And we want to see what is on the "erlang" branch compared to the "master"
    branch, running <code>git diff master erlang</code> will give us the wrong
    thing.</p>

<pre>
<b>$ git diff --stat master erlang</b>
 erlang_hw.erl |    5 +++++
 haskell.hs    |    4 ++++
 ruby.rb       |    4 ++--
 3 files changed, 11 insertions(+), 2 deletions(-)
</pre>

    <p>You see that it adds the erlang and haskell files, which is what we did
    in that branch, but then the output also reverts the changes to the ruby file
    that we did in the master branch.  What we really want to see is just the
    changes that happened in the "erlang" branch (adding the two files).  We can
    get the desired result by doing the diff from the common commit they diverged
    from:</p>

<pre>
<b>$ git diff --stat 8d585ea erlang</b>
 erlang_hw.erl |    5 +++++
 haskell.hs    |    4 ++++
 2 files changed, 9 insertions(+), 0 deletions(-)
</pre>

    <p>That's what we're looking for, but we don't want to have to figure out
    what commit the two branches diverged from every time. Luckily, Git has a
    shortcut for this. If you run <code>git diff master...erlang</code> (with        three dots in between the branch names), Git will automatically figure out
    what the common commit (otherwise known as the "merge base") of the two
    commit is and do the diff off of that.</p>

<pre>
<b>$ git diff --stat master erlang</b>
 erlang_hw.erl |    5 +++++
 haskell.hs    |    4 ++++
 ruby.rb       |    4 ++--
 3 files changed, 11 insertions(+), 2 deletions(-)
<b>$ git diff --stat master...erlang</b>
 erlang_hw.erl |    5 +++++
 haskell.hs    |    4 ++++
 2 files changed, 9 insertions(+), 0 deletions(-)
</pre>

    <p>Nearly every time you want to compare two branches, you'll want to use
    the triple-dot syntax, because it will almost always give you what you want.
    </p>

    <p>As a bit of an aside, you can also have git manually calculate the
    merge-base (first common ancestor commit) of any two commits would be with
    the <code>git merge-base</code> command:</p>

<pre>
<b>$ git merge-base master erlang</b>
8d585ea6faf99facd39b55d6f6a3b3f481ad0d3d
</pre>

    <p>So, you can do the equivalent of <code>git diff master...erlang</code>
    by running this:</p>

<pre>
<b>$ git diff --stat $(git merge-base master erlang) erlang</b>
 erlang_hw.erl |    5 +++++
 haskell.hs    |    4 ++++
 2 files changed, 9 insertions(+), 0 deletions(-)
</pre>

    <p>I would of course recommend using the easier syntax, though.</p>


    <p class="nutshell">
    <b>In a nutshell</b> you can use <code>git diff</code> to see how a project
    has changed since a known point in the past or to see what unique work is
    in one branch since it diverged from another.  Always use
    <code>git diff branchA...branchB</code> to inspect branchB relative to
    branchA to make things easier.
    </p>

  </div>
</div>

<p>And that's it!  For more information, try reading the
<a href="http://progit.org">Pro Git book</a>.</p>