CODEWITHSUNDEEP
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Reputation: 1276

How to get the tree hash of the index in git?

With git, how can I get the tree hash of the staged changes? That is, what the tree hash of the commit (not the commit hash) would be if I committed the changes?

Upvotes: 5

Views: 1109

Answers (1)

torek
torek

Reputation: 490098

The easiest way is to commit the tree:

git commit-tree

Explanation

You don't have to make a complete commit—though of course that will also work. You just need the snapshot that the commit would have.

Fortunately, the way git commit works is that it builds the commit in several stages. At one time, git commit was a simple shell script, that ran these other more-basic Git commands:1

  1. git write-tree: this takes no arguments, and—if it succeeds—makes a tree object from whatever is in the index right now, and prints the hash ID to its standard output.

  2. git commit-tree: this takes several parameters (as many parent hash IDs as you choose, and one tree hash ID) and a commit message, and builds a commit object. The commit's snapshot is the tree whose hash ID you gave it, which comes from step 1. The command prints the hash ID of the new commit object to its standard output.

  3. git update-ref: this updates a reference, such as a branch name. It takes at least two arguments: the name to update, and the new value (or a flag to indicate "delete the name").

All you want from this is step #1.

1git update-ref might be newer than the commit shell script, since in the bad old days, writing a ref just meant using an appropriate echo command. The symbolic HEAD ref was just a symbolic link. References were never packed. Once references got fancier and needed locking, git update-ref became necessary.

Upvotes: 8

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