How can I get content of a file from git index?

Question

I have a file which has been already added to my local repository. I've modified it in the working tree, so git status shows me the file as modified. I would like to know what is the file content kept in the index before I stage the file.

I can think of two ways of doing that:

1. revert a patch generated by git diff, and apply it on the file in the working tree
2. use git checkout-index, point to a temporary file and read the content from there

Is there an easier way?

Answer 1

Use the : prefix to access objects in the current index (staged but not yet commited).

git show :file

See the gitrevisions manual for more information.

Answer 2

To cat a file out of the index, I’m not sure of a preexisting scriptable way, but you can use ls-files to query the index:

$ git ls-files -s README
100644 67cfeb2016b24df1cb406c18145efd399f6a1792 0   README
$ git cat-file blob 67cfeb2016b24df1cb406c18145efd399f6a1792
# etc.

You can put the commands together like this:

git cat-file blob $(git ls-files -s README | awk '{print $2}')

(Although surely I am reinventing the wheel here.)

However, if you just want to open the original and your changes in an editor, use the difftool command. It copies the indexed version to a temporary file for you and opens vimdiff (or anything you want), and it is very flexible.

Answer 3

There are Three ways of getting diffs with git

so to see what the difference is between the file in the working directory and the index you just need to:

git diff name_of_file

I've written about this in more detail elsewhere