How can git diff be used to compare specific lines of a file across different commits?

git diff is a powerful tool that can be used to see changes between commits, branches, or even specific files. It’s a built-in function in Git that allows users to visualize the differences between various stages of a file or set of files. However, comparing specific lines of a file across different commits is a bit tricky, as git diff doesn’t directly provide this capability.

Still, you can utilize it in conjunction with other git or command line tools to achieve this. Here’s an example of how you could do this:

  1. Get the versions of the file from each commit.

First, you will want to checkout each version of the file from the commits you’re interested in:

git show <commit1>:./path/to/file > file_version1
git show <commit2>:./path/to/file > file_version2

Here, <commit1> and <commit2> are the commits you are interested in comparing, and ./path/to/file is the relative path to the file from the root of the git repository.

This will create file_version1 and file_version2 in your current directory, each containing the version of the file from each commit.

  1. Extract the lines of interest from each file.

Next, use a tool such as sed or awk to extract the specific lines you’re interested in from each version of the file. Here’s an example using sed:

sed -n '5,10p' file_version1 > file_version1_lines
sed -n '5,10p' file_version2 > file_version2_lines

This will create file_version1_lines and file_version2_lines, each containing lines 5 through 10 from each version of the file.

  1. Compare the lines from each file.

Finally, you can use diff to compare the lines from each file:

diff file_version1_lines file_version2_lines

This will print the differences between the two sets of lines to your terminal.

This method gives you a way to see the differences between specific lines across two different commits, even though git diff doesn’t directly support it.

Remember to clean up the temporary files when you’re done:

rm file_version1 file_version2 file_version1_lines file_version2_lines

These commands can be combined into a script or function to make it easier to do this in the future.