The Treeish
Besides branch heads, there are a number of shorthand ways to refer to particular objects in the Git data store. These are often referred to as a treeish. Any Git command that takes an object - be it a commit, tree or blob - as an argument can take one of these shorthand versions as well.
I will list here the most common,
but please read the
rev-parse command
for full descriptions of all the available syntaxes.
Full SHA-1
dae86e1950b1277e545cee180551750029cfe735
You can always list out the entire SHA-1 value of the object to reference it. This is sometimes easy if you're copying and pasting values from a tree listing or some other command.
Partial SHA-1
dae86e
Just about anything you can reference with the full SHA-1 can be referenced fine with the first 6 or 7 characters. Even though the SHA-1 is always 40 characters long, it's very uncommon for more than the first few to actually be the same. Git is smart enough to figure out a partial SHA-1 as long as it's unique.
Branch or Tag Name
master
Anything in .git/refs/heads or .git/refs/tags can be used to refer to the commit it points to.
Date Spec
master@{yesterday}
master@{1 month ago}
This example would refer to the value of that branch yesterday. Importantly, this is the value of that branch in your repository yesterday. This value is relative to your repo - your 'master@{yesterday}' will likely be different than someone else's, even on the same project, whereas the SHA-1 values will always point to the same commit in every copy of the repository.
Ordinal Spec
master@{5}
This indicates the 5th prior value of the master branch. Like the Date Spec, this depends on special files in the .git/log directory that are written during commits, and is specific to your repository.
Carrot Parent
e65s46^2
master^2
This refers to the Nth parent of that commit. This is only really helpful for commits that merged two or more commits - it is how you can refer to a commit other than the first parent.
Tilde Spec
e65s46~5
The tilde character, followed by a number, refers to the Nth generation grandparent of that commit. To clarify from the carrot, this is the equivalent commit in caret syntax:
e65s46^^^^^
Tree Pointer
e65s46^{tree}
This points to the tree of that commit.
Any time you add a ^{tree} to any commit-ish,
it resolves to its tree.
Blob Spec
master:/path/to/file
This is very helpful for referring to a blob under a particular commit or tree.