DIY_GIT_in_Python/how_to/Change_20.md

• tag: Implement CLI command

Now that we have branching history we have some OIDs we need to keep track of. Assume we have two branches (continuing from the example we had for checkout):

o-----o-----o-----o-----@-----@-----@
^                  \                ^
first commit        ----$-----$     6c9f80a187ba39b4...
                              ^
                              d8d43b0e3a21df0c...

If we want to switch back and forth between the two “branches” with checkout, we need to remember both OIDs, which are quite long.

To make our lives easier, let’s implement a command to attach a name to an OID. Then we’ll be able to refer to the OID by that name.

The end result will look like this:

$ # Make some changes
...
$ ugit commit
d8d43b0e3a21df0c845e185d08be8e4028787069
$ ugit tag my-cool-commit d8d43b0e3a21df0c845e185d08be8e4028787069
$ # Make more changes
...
$ ugit commit
e549f09bbd08a8a888110b07982952e17e8c9669

$ ugit checkout my-cool-commit
        or
$ ugit checkout d8d43b0e3a21df0c845e185d08be8e4028787069

The last two commands are equivalent, because “my-cool-commit” is a tag that points to d8d43b0e3a21df0c845e185d08be8e4028787069.

We will implement this in a few steps. The first step is to create a CLI commmand that call the relevant command in the base module. The base module does nothing at this stage.