Some notes on terminology

In case you’re not familiar with some of the terminology used below, here is a small glossary.

Object

An object in Git is either a blob (file), tree (directory), commit, or tag. All objects in Git have a hash (like 99b69df491c0bcf5262a967313fad8be0098352e) and are connected in a way that allows them to be modelled as a directed acyclic graph.

Reference

A reference in Git is a bit like a pointer, or a symlink. References are not objects themselves, and they always point to either an object or another reference. Branches, tags, and HEAD are examples of references.

You can learn about all of this and much more in my Hacker’s Guide to Git.

Show the contents of a file at a specific commit

# Show the contents of hello.txt at 0f64e9e
$ git show 0f64e9e:hello.txt
Hello, world!

Find which commit a reference points at

# Show the full commit hash for "feature-branch-1"
$ git rev-parse feature-branch-1
0f64e9e759c904553309858070f444e5e64847c4

$ git rev-parse --short feature-branch-1
0f64e9e

Find which branches a commit is in

# Show the branches containing 0f64e9e
$ git branch --contains 0f64e9e
  master
* other-branch

Find commits that are in one branch but not another

# Show commits that are in hotfix-1 but not master
$ git log --right-only master...hotfix-1

0f64e9e Apply hotfix patch from #2914 to hotfix-1
bc3bff5 [Cherry-pick] Fix issue #2926
Exclude commits that were cherry-picked
# Show non-cherry-picked commits that are in hotfix-1 but not master
$ git log --cherry-pick --right-only master...hotfix-1

0f64e9e Apply hotfix patch from #2914 to hotfix-1

View details of an object

# Show the full details of the 0f64e9e commit
$ git cat-file -p 0f64e9e
tree af22d0482b89640c95986f3b4663026bcb7f764b
parent bc3bff555f573ac76f0d3e71f0e54d63f50b8434
author Foo Bar <foo@bar.com> 1436294582 +0100
committer Foo Bar <foo@bar.com> 1436294582 +0100

Lorem ipsum dolor sit amet, consectetur adipiscing elit
Show an object’s type
$ git cat-file -t 0f64e9e
commit
Show an object’s size
$ git cat-file -s 0f64e9e
253

# -t will show tree entries, and -r will recurse into sub-trees
$ git ls-tree -t -r HEAD
100644 blob 59e004af21a725c9b378001a1b231967f955b992    .gitignore
100644 blob 9f5d366d261317d8ff881ee2945ef2c7960fa2ea    .travis.yml
100644 blob 148fc67781eba8c08bbb4db1fc9e92b9781ec28d    LICENSE
100644 blob 4a2727bb9afae5782510e7ce764608540dd7c04a    Makefile
100644 blob b07b8d5f39d6f62a18a1b0791f33a784ec34556e    README.md
100644 blob 9a994af677b0dfd41b4e3b76b3e7e604003d64e1    Setup.hs
100644 blob 66820894ca2c16725e8527e16785f2eebd89871a    lishp.cabal
040000 tree eda8357ddb73fa384f283291bac84d7fe1bce436    src
040000 tree 6a84cb52f17c7e1ff691fe45f4c70df5269bdab0    src/Lishp
100644 blob 1f7677ed0c7f3e713c7e6a16d94cc3db89d911cd    src/Lishp/Interpreter.hs
100644 blob 1a0fe9394bc2d7789d783a467626301204de700a    src/Lishp/Primitives.hs
100644 blob caf0fcf1cd265436efbaa6cc39338e653197a3ee    src/Lishp/Readline.hs
100644 blob 92cf693d29169066356bed3f1ae794a624db49a5    src/Lishp/Types.hs
100644 blob 82ec4d14e01598f38a083ab2dea326615cd048dd    src/Main.hs
040000 tree ba0974cba2e671b840bb3cefa69569f62cec29b5    test
100644 blob 2589b7aeb1562a3aa951c2fa52f64891db87d1c6    test/assignment.sh
100644 blob d54fa0437e13ba5ee15ad13330ac07b9a6abcdcc    test/equality.sh
100644 blob ee61aa5dffca43032b5aeef6f4e79ff1f9f2df85    test/functions.sh
100644 blob 22fbec9189d2641c590836c4bb19431d3c6d3df3    test/primitives.sh
100644 blob c455f01b3d88b5d510ff4ebb50e93c5d7f8f0b26    test/types.sh

Find the first tag which contains a reference

$ git describe HEAD
v1.6.1

Find dangling or unreachable objects

$ git fsck --lost-found
Checking object directories: 100% (256/256), done.
Checking objects: 100% (153/153), done.
dangling blob b3cc2f0f4666fda6cda0f6527facbb5a7579d29e
dangling commit a621c6a60383ee430c6d21333026dd5aa7a895b0
dangling commit 4c0aab20fa5e6ba1ede09efbd9015dd8d1c54228
dangling blob 6af75568b0a8aee29c47125098b4b6d60a6a8a6f