Git tree objects.

2024-03-02 05:12:57 -07:00 · 2024-03-02 05:12:57 -07:00 · d27412d5c7
parent 3cc9d74d05
commit d27412d5c7
3 changed files with 285 additions and 28 deletions
--- a/notes/.obsidian/plugins/obsidian-to-anki-plugin/data.json
+++ b/notes/.obsidian/plugins/obsidian-to-anki-plugin/data.json
@ -181,7 +181,7 @@
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@ -217,14 +217,15 @@
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    "filesystems/cas.md": "34906013a2a60fe5ee0e31809b4838aa",
-    "git/objects.md": "b49015b8ebffc2c976d97b2484c74448",
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    "Basic": [
--- a/notes/_journal/2024-03-01.md
+++ b/notes/_journal/2024-03-01.md
@ -12,4 +12,5 @@ title: "2024-03-01"

 * Reviewed database reading/videos from yesterday with Kevin.
 * Finished planning soft skills course with Gus.
-* Added flashcards around sequences.
+* Added flashcards around sequences.
+* Added flashcards for git trees.
--- a/notes/git/objects.md
+++ b/notes/git/objects.md
@ -10,6 +10,8 @@ tags:

 ## Overview

+Git has a few fundamental types that serve as the foundation for its [[cas|CAS]] system, expanded upon in each subsequent section.
+
 %%ANKI
 Basic
 What cryptographic hash function does git use internally?
@ -106,22 +108,6 @@ Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Soft
 <!--ID: 1709177255627-->
 END%%

-%%ANKI
-Basic
-What plumbing subcommand is used to generate an oid?
-Back: `hash-object`
-Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
-<!--ID: 1709177255632-->
-END%%
-
-%%ANKI
-Basic
-The `hash-object` subcommand optionally stores the resulting object in what directory?
-Back: `.git/objects`
-Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
-<!--ID: 1709177255637-->
-END%%
-
 %%ANKI
 Cloze
 The {object database} refers to the {`.git/objects`} directory.
@ -129,10 +115,132 @@ Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Soft
 <!--ID: 1709177255644-->
 END%%

+%%ANKI
+Basic
+Where does e.g. `d670460b4b4aece5915caf5c68d12f560a9fe3e4` live in the object database?
+Back: At `.git/objects/d6/70460b4b4aece5915caf5c68d12f560a9fe3e4`.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255668-->
+END%%
+
+%%ANKI
+Basic
+What regular files exist in the object database after `git init`?
+Back: None.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255672-->
+END%%
+
+%%ANKI
+Basic
+Files in the object database are compressed using what format?
+Back: The `zlib` data format.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709345254695-->
+END%%
+
+%%ANKI
+Basic
+What compression library does git use internally?
+Back: `zlib`
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709345254701-->
+END%%
+
+%%ANKI
+Basic
+How do you decode e.g. `.git/objects/d6/70460b4b4aece5915caf5c68d12f560a9fe3e4`?
+Back: By decompressing the `zlib` data formatted file.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709345254705-->
+END%%
+
+%%ANKI
+Basic
+What plumbing subcommand is used to inspect git objects?
+Back: `cat-file`
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709345254709-->
+END%%
+
+%%ANKI
+Basic
+What plumbing subcommand is typically used over manually decompressing with `zlib`?
+Back: `cat-file`
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709345254713-->
+END%%
+
+%%ANKI
+Basic
+What is the difference in output of manually decompressing `<OID>` and the following?
+```bash
+$ git cat-file -p <OID>
+```
+Back: Manual decompression includes the object header.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709345254716-->
+END%%
+
+## Blobs
+
+The **b**inary **l**arge **ob**ject (blob) is used to represent arbitrary files.
+
+%%ANKI
+Basic
+Why are git blobs named the way they are?
+Back: It is an acronym for **b**inary **l**arge **ob**ject.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709345254720-->
+END%%
+
+%%ANKI
+Basic
+A regular file is stored as what kind of git object?
+Back: A blob.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709345254723-->
+END%%
+
+%%ANKI
+Basic
+What does the decompressed header of a blob object look like?
+Back: `blob <size><NUL>`
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709345254726-->
+END%%
+
+%%ANKI
+Basic
+What is the value of `<size>` found in the header of a blob file?
+Back: The number of bytes of the decompressed content.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709345254730-->
+END%%
+
+%%ANKI
+Basic
+What is the decompressed text of the blob generated by the following?
+```bash
+$ echo -n "abcd" | git hash-object -w --stdin
+```
+Back: `blob 4\0abcd`
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709345254733-->
+END%%
+
+%%ANKI
+Basic
+The `hash-object` subcommand optionally stores a created object in what directory?
+Back: `.git/objects`
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709177255637-->
+END%%
+
 %%ANKI
 Basic
 What does the `hash-object` subcommand return?
-Back: The computed object id.
+Back: The oid of the new blob object.
 Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
 <!--ID: 1709177255651-->
 END%%
@ -155,18 +263,165 @@ END%%

 %%ANKI
 Basic
-Where does object e.g. `d670460b4b4aece5915caf5c68d12f560a9fe3e4` live in the object database?
-Back: At `.git/objects/d6/70460b4b4aece5915caf5c68d12f560a9fe3e4`.
+What is the result of the following command?
+```bash
+$ echo -n "abcd" | git hash-object --stdin
+```
+Back: An oid (usually a SHA-1 hash).
 Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
-<!--ID: 1709177255668-->
+<!--ID: 1709345254736-->
 END%%

 %%ANKI
 Basic
-What regular files exist in the object database after `git init`?
-Back: None.
+What plumbing subcommand is used to create blobs?
+Back: `hash-object`
 Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
-<!--ID: 1709177255672-->
+<!--ID: 1709348481684-->
+END%%
+
+## Trees
+
+The tree is used to represent directories. It maintains filenames of any contained blobs.
+
+%%ANKI
+Basic
+What git object maintains filenames?
+Back: Trees.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709348481689-->
+END%%
+
+%%ANKI
+Basic
+A directory is stored as what kind of git object?
+Back: Trees.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709348481693-->
+END%%
+
+%%ANKI
+Basic
+All the *content* of a git repository is stored as what kind of git objects?
+Back: Trees and blobs.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709348481696-->
+END%%
+
+%%ANKI
+Cloze
+A regular file is to {blob} objects as directories are to {tree} objects.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709345254740-->
+END%%
+
+%%ANKI
+Cloze
+{`hash-object`} is to blobs as {`write-tree`} is to trees.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709348481699-->
+END%%
+
+%%ANKI
+Basic
+What does the decompressed header of a tree object look like?
+Back: `tree <size><NUL>`
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709348481704-->
+END%%
+
+%%ANKI
+Basic
+What does the decompressed header of an empty tree object look like?
+Back: `tree 0<NUL>`
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709348481711-->
+END%%
+
+%%ANKI
+Basic
+What plumbing subcommand is used to create trees?
+Back: `write-tree`
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709348481715-->
+END%%
+
+%%ANKI
+Basic
+The `write-tree` subcommand stores the new tree object in what directory?
+Back: `.git/objects`
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709348481718-->
+END%%
+
+%%ANKI
+Basic
+The `write-tree` subcommand creates a tree object from what?
+Back: The current index.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709348481721-->
+END%%
+
+%%ANKI
+Basic
+What does the `write-tree` subcommand return?
+Back: The oid of the new tree object.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709348481725-->
+END%%
+
+%%ANKI
+Basic
+Why doesn't `write-tree` take any arguments?
+Back: It creates a new tree from the current index.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709348481730-->
+END%%
+
+%%ANKI
+Basic
+What plumbing subcommand is used to put tree objects into the staging area?
+Back: `read-tree`
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709349279634-->
+END%%
+
+%%ANKI
+Basic
+How does the following command update the index?
+```bash
+$ git read-tree d8329fc1cc938780ffdd9f94e0d364e0ea74f579
+```
+Back: It adds the contents of tree `d8329fc1cc938780ffdd9f94e0d364e0ea74f579`.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709349279641-->
+END%%
+
+%%ANKI
+Basic
+How does the following command update the index?
+```bash
+$ git read-tree --prefix=foo d8329fc1cc938780ffdd9f94e0d364e0ea74f579
+```
+Back: It adds tree `d8329fc1cc938780ffdd9f94e0d364e0ea74f579` as subtree `foo`.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709349279646-->
+END%%
+
+%%ANKI
+Basic
+Where does the `read-tree` subcommand read the tree into?
+Back: The current index.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709349279652-->
+END%%
+
+%%ANKI
+Basic
+The `read-tree` and `write-tree` interact indirectly through what?
+Back: The staging area.
+Reference: Scott Chacon, *Pro Git*, Second edition, The Expert’s Voice in Software Development (New York, NY: Apress, 2014).
+<!--ID: 1709349279660-->
 END%%

 ## References