Creating Blobs
Creating a blob in your Git repository and getting a SHA back is pretty easy. The git hash-object command is all you’ll need. To create a blob object from an existing file, just run it with the ‘-w’ option (which tells it to write the blob, not just compute the SHA).<\/p>\n\n\n\n
$ git hash-object -w myfile.txt
6ff87c4664981e4397625791c8ea3bbb5f2279a3<\/p>\n\n\n\n
$ git hash-object -w myfile2.txt
3bb0e8592a41ae3185ee32266c860714980dbed7
The STDOUT output of the command will the the SHA of the blob that was created.<\/p>\n\n\n\n
Creating Trees
Now lets say you want to create a tree from your new objects. The git mktree command makes it pretty simple to generate new tree objects from git ls-tree formatted output. For example, if you write the following to a file named ‘\/tmp\/tree.txt’ :<\/p>\n\n\n\n
100644 blob 6ff87c4664981e4397625791c8ea3bbb5f2279a3 file1
100644 blob 3bb0e8592a41ae3185ee32266c860714980dbed7 file2
and then piped that through the git mktree command, Git will write a new tree to the object database and give you back the new sha of that tree.<\/p>\n\n\n\n
$ cat \/tmp\/tree.txt | git mk-tree
f66a66ab6a7bfe86d52a66516ace212efa00fe1f
Then, we can take that and make it a subdirectory of yet another tree, and so on. If we wanted to create a new tree with that one as a subtree, we just create a new file (\/tmp\/newtree.txt) with our new SHA as a tree in it:<\/p>\n\n\n\n
100644 blob 6ff87c4664981e4397625791c8ea3bbb5f2279a3 file1-copy
040000 tree f66a66ab6a7bfe86d52a66516ace212efa00fe1f our_files
and then use git mk-tree again:<\/p>\n\n\n\n
$ cat \/tmp\/newtree.txt | git mk-tree
5bac6559179bd543a024d6d187692343e2d8ae83
And we now have an artificial directory structure in Git that looks like this:<\/p>\n\n\n\n
|– file1-copy 1 directory, 3 files Rearranging Trees First, we read the tree into our index file under a new prefix using the git read-tree command, and then write the index contents as a tree using the git write-tree command:<\/p>\n\n\n\n $ export GIT_INDEX_FILE=\/tmp\/index $>git ls-tree bb2fa Creating Commits GIT_AUTHOR_NAME $ git commit-tree bb2fa < \/tmp\/message Creating BlobsCreating a blob in your Git repository and getting a SHA back is pretty easy. The git hash-object command is all you’ll need. To create a blob object from… <\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_joinchat":[],"footnotes":""},"categories":[2],"tags":[],"class_list":["post-30833","post","type-post","status-publish","format-standard","hentry","category-uncategorised"],"_links":{"self":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts\/30833","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/comments?post=30833"}],"version-history":[{"count":1,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts\/30833\/revisions"}],"predecessor-version":[{"id":30834,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts\/30833\/revisions\/30834"}],"wp:attachment":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/media?parent=30833"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/categories?post=30833"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/tags?post=30833"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}-- our_files |-- file1 <\/code>— file2<\/p>\n\n\n\n
without that structure ever having actually existed on disk. Plus, we have a SHA (5bac6559) that points to it.<\/p>\n\n\n\n
We can also do tree manipulation by combining trees into new structures using the index file. As a simple example, let’s take the tree we just created and make a new tree that has two copies of our 5bac6559 tree in it using a temporary index file. (You can do this by resetting the GIT_INDEX_FILE environment variable or on the command line)<\/p>\n\n\n\n
$ git read-tree –prefix=copy1\/ 5bac6559
$ git read-tree –prefix=copy2\/ 5bac6559
$ git write-tree
bb2fa6de7625322322382215d9ea78cfe76508c1<\/p>\n\n\n\n
040000 tree 5bac6559179bd543a024d6d187692343e2d8ae83 copy1
040000 tree 5bac6559179bd543a024d6d187692343e2d8ae83 copy2
So now we can see that we’ve created a new tree just from index manipulation. You can also do interesting merge operations and such in a temporary index this way – see the git read-tree docs for more information.<\/p>\n\n\n\n
Now that we have a tree SHA, we can create a commit object that points to it. We can do this using the git commit-tree command. Most of the data that goes into the commit has to be set as environment variables, so you’ll want to set the following:<\/p>\n\n\n\n
GIT_AUTHOR_EMAIL
GIT_AUTHOR_DATE
GIT_COMMITTER_NAME
GIT_COMMITTER_EMAIL
GIT_COMMITTER_DATE
Then you will need to write your commit message to a file or somehow pipe it into the command through STDIN. Then, you can create your commit object based on the tree sha we have.<\/p>\n\n\n\n
a5f85ba5875917319471dfd98dfc636c1dc65650
If you want to specify one or more parent commits, simply add the shas on the command line with a ‘-p’ option before each. The SHA of the new commit object will be returned via STDOUT.<\/p>\n","protected":false},"excerpt":{"rendered":"