Git diff with line numbers (Git log with line numbers)

Question

When I do a git diff or a git log -p, how do I get line numbers of the source file(s) inlined with the output?

I tried to look it up

Answer 1

A quick way is to use git diff -U0. That will set the lines of context to 0, which will make the @@ values match the actual changed lines. By default, the @@ values include 3 lines of before/after context, which is not convenient for humans.

Example:

git diff # default
@@ -10,8 +10,8 @@

This is hard to calculate the line numbers of the changed lines because line 10 refers to the first line of the before context. The actual line number of the first changed line is 10+3=13. To calculate the number of changed lines, then you have to also subtract the before and after context: 8-3-3=2.

git diff -U0
@@ -13,2 +13,2 @@

As you can see, setting context = 0 makes the @@ values easier for humans to read. You can see that the changed lines start at line 13, and there are 2 changed lines.

This isn't perfect, since it only shows the line number for each block. If you want to see line numbers for every line, then use difftool for an external editor. See https://stackoverflow.com/a/50049752

Answer 2

As of 24 May 2020, you can now use the third-party tool git diffn (full disclosure: I wrote it) for this purpose. It's a light-weight wrapper around git diff, written in the awk pattern/action-based programming language. Here's a sample output from running git diffn:

1/3: What is it?

From the top of git-diffn.sh:

DESCRIPTION:

git-diffn.sh

1. a drop-in replacement for git diff which also shows line 'n'umbers! Use it exactly like git diff, except you'll see these beautiful line numbers as well to help you make sense of your changes.

2. since it's just a light-weight awk-language-based wrapper around git diff, it accepts ALL options and parameters that git diff accepts. Examples:

3. git diffn HEAD~

4. git diffn HEAD~3..HEAD~2

5. works with any of your git diff color settings, even if you are using custom colors

6. See my answer here for how to set custom diff colors, as well as to see a screenshot of custom-color output from git diffn: How do you customize the color of the diff header in git diff?

7. Here are some sample git config commands from my answer above to set custom git diff colors and attributes (text formatting):

      git config --global color.diff.meta "blue"
      git config --global color.diff.old "black red strike"
      git config --global color.diff.new "black green italic"
      git config --global color.diff.context "yellow bold"
   

8. in git diffn, color output is ON by default; if you want to disable the output color, you must use --no-color or --color=never. See man git diff for details. Examples:

    git diffn --color=never HEAD~
    git diffn --no-color HEAD~3..HEAD~2
   

2/3: Installation

1. Windows (untested): this may work inside the bash terminal that comes with Git for Windows, but is untested. Install Git for Windows. Open the bash terminal it comes with, and try to follow the instructions below. I need some testers who will test this in Git for Windows. Please see and answer here: https://github.com/git-for-windows/git/issues/2635.
2. Mac (untested): use the terminal and follow the instructions below. You may need to install gawk. If so, try this: brew install gawk.
3. Linux (tested on Ubuntu 18.04 and works perfectly): follow the terminal instructions below.

Option 1 (my recommendation): download the whole repo and then create a symlink to the program so that you can easily receive updates by doing a git pull from the repo whenever you want.

First, cd to wherever you want to install this. Then run:

git clone https://github.com/ElectricRCAircraftGuy/eRCaGuy_dotfiles.git
cd eRCaGuy_dotfiles/useful_scripts
mkdir -p ~/bin
ln -si "${PWD}/git-diffn.sh" ~/bin/git-diffn

Done! Now just do the final step below!

Option 2 (for those who just want the 1 file): download just the one file one time.

mkdir -p ~/bin
cd ~/bin
wget https://raw.githubusercontent.com/ElectricRCAircraftGuy/eRCaGuy_dotfiles/master/useful_scripts/git-diffn.sh
chmod +x git-diffn.sh
mv git-diffn.sh git-diffn

Done! Now just do the final step below!

Final step:

Now close and re-open your terminal, or re-source it with . ~/.bashrc, and you are done!

git diffn will now work as an exact drop-in replacement for git diff!

Here's a demo:

3/3: Demo of git diffn:

Create this file:

hello_world.c:

#include <stdio.h>

int main()
{
    printf("Hello World\n");

    return 0;
}

Commit it:

git add hello_world.c
git commit -m "add hello_world.c"

Change it to this and save the file:

hello_world.c:

// Basic hello world example

#include <stdio.h>

int main(int argc, char *argv[])
{
    printf("Hello Gabriel\n");
    
    int i = 700;
    printf("i = %i\n", i);
    return 0;
}

Now run:

git diff

Here's the output of git diff first for comparison purposes:

$ git diff
diff --git a/hello_world.c b/hello_world.c
index e01704a..e971b73 100644
--- a/hello_world.c
+++ b/hello_world.c
@@ -1,8 +1,12 @@
+// Basic hello world example
+
 #include <stdio.h>
 
-int main()
+int main(int argc, char *argv[])
 {
-    printf("Hello World\n");
-
+    printf("Hello Gabriel\n");
+    
+    int i = 700;
+    printf("i = %i\n", i);
     return 0;
-}
\ No newline at end of file
+}

And a screenshot to show the color. Note that the red highlighted section is simply showing empty whitespace (spaces in this case) that could be deleted:

Now here's the output of git diffn. Notice it shows all line numbers perfectly!

• Line numbers for deleted lines are on the left, and show a - sign on both the far left AND to the right of the : to help you see better--whether your eyes like to scan down to the right of the colon or down on the far left of the screen.
• Line numbers for added lines are farther to the right, and show a + sign on both the far left AND to the right of the :.
• Line numbers for unchanged lines shown for context are shown for both the left (old file) AND the right (new file), separated by a ,.

Output of git diffn:

$ git diffn
diff --git a/hello_world.c b/hello_world.c
index e01704a..e971b73 100644
--- a/hello_world.c
+++ b/hello_world.c
@@ -1,8 +1,12 @@
+        1:+// Basic hello world example
+        2:+
    1,   3: #include <stdio.h>
    2,   4: 
-   3     :-int main()
+        5:+int main(int argc, char *argv[])
    4,   6: {
-   5     :-    printf("Hello World\n");
-   6     :-
+        7:+    printf("Hello Gabriel\n");
+        8:+    
+        9:+    int i = 700;
+       10:+    printf("i = %i\n", i);
    7,  11:     return 0;
-   8     :-}
\ No newline at end of file
+       12:+}

And a screenshot to show the color. Notice that the colons are NOT colored or stylized to match the surrounding text on the left and right. This is intentional and designed-in behavior to act as a visual separator between the line numbers added on the left and the original git diff output on the right.

Answer 3

First, config your git diff tool, e.g. Meld

git config --global diff.tool meld

Then, yank your difftool on some file:

git difftool -y config.rb

Remember setting line number in your diff tool's preference.