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World 10: Deep Git

Plumbing vs porcelain

You will learn: Git's two kinds of commands, and how to save a blob by hand.

The problem

Your script needs the newest commit id. git log prints too much, and its look can change. What should the script use?

Watch

Low-level commands are plumbing: Git's low-level commands, like cat-file. Plain, steady output for scripts.: the pipes under the sink. They print plain, steady output. Scripts love them.

Try it

The shiny sink on top is porcelain: Git's friendly everyday commands, like status and commit.: commands for people. Sort each command.

Drag a card into a box. Or tap the card, then tap the box.

      Watch

      git hash-object prints the id Git would give a file. It matches the blob already in the commit. Same content, same id.

      Try it

      notes.txt is not in Git yet. Save its content as a blob, with no commit. Then read the blob back.

      Predict

      Ben has the same notes.txt on his laptop. He runs git hash-object notes.txt. What id does he get?

      Check

      Build the command that prints index.html as the newest commit saved it.

      Tap the pieces in the right order.

      …

      You did it!

      You can now tell plumbing from porcelain and save a blob yourself.

      Go deeper (optional)

      Porcelain output may change between Git versions. Plumbing output stays steady. Need status in a script? git status --porcelain gives a format that is promised to stay the same. git ls-tree -r --name-only HEAD lists every file in a commit.