CODEWITHSUNDEEP
git
graywolf
graywolf

Reputation: 7470

Getting SHA hash of file in specific commit

How can I get SHA hash of a file in specified commit? I can get all commits that touched the file using git log file, but how can I get SHA hash of a file in each particular commit?

I think I can do it by checking out the commit and than use git-hash-object, but there must be easier way.

Upvotes: 5

Views: 6154

Answers (3)

Greg Bacon
Greg Bacon

Reputation: 139411

git show and git log are close cousins and share options. Your question asked about the SHA-1 object name of a file associated with a particular commit but then also for the same information for each commit along the way in the history.

The --raw option gives the information you’re after. The examples below will use git’s own repository.

To show the files that changed with a particular commit, use git show or git log -1. The latter will not generate output for the tag object but the tagged commit only.

$ git log -1 --raw v2.8.1
commit d95553a6b8c5153f541adcfc3346004e8249b0e6
Author: Junio C Hamano <[email protected]>
Date:   Sun Apr 3 10:11:35 2016 -0700

    Git 2.8.1

    Signed-off-by: Junio C Hamano <[email protected]>

:000000 100644 0000000... ef6d80b... A  Documentation/RelNotes/2.8.1.txt
:100644 100644 adc940b... 8afe349... M  Documentation/git.txt
:100755 100755 4e9450b... 46595da... M  GIT-VERSION-GEN
:120000 120000 7db3040... d40c3e1... M  RelNotes

Each change line contains

  • beginning or source mode (000000 indicates created or unmerged)
  • resulting or destination mode (000000 indicates deleted or unmerged)
  • source SHA-1 (all zeros for creation)
  • destination SHA-1 (all zeros for deletion)
  • status code plus optional numeric score (above A is addition and M modification)
  • path

See “Raw output format” in git diff’s documentation for the full details.

The SHA-1 object name for the file RelNotes associated with the v2.8.1 tag is d40c3e1, which we can verify and expand to all forty digits with

$ git rev-parse v2.8.1:RelNotes
d40c3e126c03b0e4bd9c6162f63a35a45f5e9020

To show hashes for RelNotes, which is a symbolic link that points to the under Documentation/RelNotes that corresponds to a given version, along the way in version 2.8.1’s history:

$ git log --raw v2.8.1 -- RelNotes
commit d95553a6b8c5153f541adcfc3346004e8249b0e6
Author: Junio C Hamano <[email protected]>
Date:   Sun Apr 3 10:11:35 2016 -0700

    Git 2.8.1

    Signed-off-by: Junio C Hamano <[email protected]>

:120000 120000 7db3040... d40c3e1... M  RelNotes

commit c9906e47c065940bfe1a9992da494a8f437a49ac
Author: Junio C Hamano <[email protected]>
Date:   Tue Jan 12 15:20:51 2016 -0800

    First batch for post 2.7 cycle

    Signed-off-by: Junio C Hamano <[email protected]>

:120000 120000 3ba13ce... 7db3040... M  RelNotes

commit 24a00ef646974be49ef7138239c3803805400797
Author: Junio C Hamano <[email protected]>
Date:   Mon Oct 5 12:58:10 2015 -0700

    Start cycle toward 2.7

    Signed-off-by: Junio C Hamano <[email protected]>

:120000 120000 def6ebd... 3ba13ce... M  RelNotes
[...]

Use the --abbrev option to get all forty hex digits of the hash. Here the output will appear extra chatty because the output of git show covers both the v2.8.1 tag and the commit to which v2.8.1 points.

$ git show --raw --abbrev=40 v2.8.1
tag v2.8.1
Tagger: Junio C Hamano <[email protected]>
Date:   Sun Apr 3 10:14:32 2016 -0700

Git 2.8.1
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1
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=NLvn
-----END PGP SIGNATURE-----

commit d95553a6b8c5153f541adcfc3346004e8249b0e6
Author: Junio C Hamano <[email protected]>
Date:   Sun Apr 3 10:11:35 2016 -0700

    Git 2.8.1

    Signed-off-by: Junio C Hamano <[email protected]>

:000000 100644 0000000000000000000000000000000000000000 ef6d80b008a0a7970238404b034593be27e933c3 A      Documentation/RelNotes/2.8.1.txt
:100644 100644 adc940bf7591069c74c9b47aa5e5686e0438d606 8afe349781d57527083fdb75511959fd25a4239b M      Documentation/git.txt
:100755 100755 4e9450b3ae0c403820f0166435c52c4ea74e7451 46595dad2234f861198347ef8f4f60d167061709 M      GIT-VERSION-GEN
:120000 120000 7db30403c3471e15f4f15a5e68016d7926b3e3de d40c3e126c03b0e4bd9c6162f63a35a45f5e9020 M      RelNotes

The SHA-1 object name of a blob (how git represents file contents) is not identical to running sha1sum on the file because git adds metadata to the front: the literal string blob, followed by a space, followed by the length of the content in decimal, and terminated with a NUL byte. To compute a SHA-1 hash of the contents of successive versions of a file going backward in time, use a command along the lines of

$ for commit in $(git log --pretty=%H v2.8.1 -- RelNotes | head -3) ; \
    do git show ${commit}:RelNotes | sha1sum ; \
  done
ce5501f9daadf110a20a4e4eccdfed63ef4b27e3  -
bd4d920214c4a48d8820292e24f020690595858d  -
5d47b511d86abd490fa4f2c2a8d4ef3589e1aecf  -

With --pretty=%H and -- RelNotes we tell git that we want only the SHA-1 hashes of commits that touch RelNotes (limited to the three most recent with head -3). Then for each of those commits, we feed the tracked content to sha1sum.

If you prefer xargs, it looks like

$ git log --pretty=%H v2.8.1 -- RelNotes | head -3 |
    xargs -I {} sh -c 'git show {}:RelNotes | sha1sum'
ce5501f9daadf110a20a4e4eccdfed63ef4b27e3  -
bd4d920214c4a48d8820292e24f020690595858d  -
5d47b511d86abd490fa4f2c2a8d4ef3589e1aecf  -

Upvotes: 6

torek
torek

Reputation: 487705

There is a very quick way to get the Git hash for a file within some commit:

git rev-parse <commit-ID>:/path/to/file

Git's hash is a SHA-1 of the word blob followed by a space, followed by a decimal ASCII string giving the size of the file in bytes, followed by a NUL byte, followed by the file's contents:

size=$(wc -c $file)
(printf "blob %d\0" $size; cat $file) | sha1sum -

It looks from comments, though, like you want an actual SHA-1 of the file's contents (as someone else would get by extracting the file and running sha1sum on it), and not the git hash:

git show <commit-ID>:path | sha1sum -

is the general (non-bash-specific) method (bash's <( is fine as well, just make sure you have the fdesc file system mounted).

Upvotes: 7

zebediah49
zebediah49

Reputation: 7611

At a minimum, you don't need to check out the commit. git show can directly show you an object, including a blob. You can send that into git hash-object without ever checking it out.

I think there should be a more efficient way, but you can do

git hash-object <(git show [commit]:[path])

So, for example,

$ git hash-object <(git show master:Makefile)
3fb4e1cbe0019c691a504e3419ece252db6f60ab

Upvotes: 1

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