Background

Having written the second post in this series, I thought that I understood how to compute the SHA-1 hash of Git tree objects.

Problem

Suppose that I add a file named rose which consisted merely of the word sweet and a line terminator to the folder hello in the second post in this series. I include the setup here for convenience.

$ mkdir hello && cd hello
$ git init
$ echo "hello world" > hello.txt
$ git add hello.txt
$ git write-tree
68aba62e560c0ebc3396e8ae9335232cd93a3f60
$ echo "sweet" > rose
$ git add rose
$ git write-tree
b12767ff2f8a8160bca15abfb775bca5ba31ccf1
$ git cat-file -p b12767ff2f8a8160bca15abfb775bca5ba31ccf1 | tee test.txt
100644 blob 3b18e512dba79e4c8300dd08aeb37f8e728b8dad    hello.txt
100644 blob aa823728ea7d592acc69b36875a482cdf3fd5c8d    rose

Therefore, our target hash is b12767ff2f8a8160bca15abfb775bca5ba31ccf1.

Just like what I’d done in the previous post, I manually changed the hashes into a printf command that writes out the binary value of the hashes.

# Note: I *didn't* type enter in the following command.  Just keep typing.
$ printf "tree 70\x00100644 hello.txt\x00\x3b\x18\xe5\x12\xdb\xa7\x9e\x4c\x83\x0
0\xdd\x08\xae\xb3\x7f\x8e\x72\x8b\x8d\xad\n100644 rose\x00\xaa\x82\x37\x28\xea\x
7d\x59\x2a\xcc\x69\xb3\x68\x75\xa4\x82\xcd\xf3\xfd\x5c\x8d" | shasum
a4b430f9da3e22c0854fb26c97da77db271e5acf  -

What I got is a4b430f9da3e22c0854fb26c97da77db271e5acf, which is different from the target. How can I get back the right SHA-1 hash?

Method

I read domegetter’s comment on this Gist, and removed the newline character \n in the middle of the quoted string in the above printf command. Then I decreased the object size by one since a character had been taken out.

# Note: I *didn't* type enter in the following command.  Just keep typing.
$ printf "tree 69\x00100644 hello.txt\x00\x3b\x18\xe5\x12\xdb\xa7\x9e\x4c\x83\x0
0\xdd\x08\xae\xb3\x7f\x8e\x72\x8b\x8d\xad100644 rose\x00\xaa\x82\x37\x28\xea\x7d
\x59\x2a\xcc\x69\xb3\x68\x75\xa4\x82\xcd\xf3\xfd\x5c\x8d" | shasum
b12767ff2f8a8160bca15abfb775bca5ba31ccf1  -

We’re done!