Is "git log --pretty=<pretty format>" a porcelain or plumbing command?

Question

I am creating some scripts and programs that fetch commit information using

git log --pretty=<my format> -1 <commit>

I wonder if the output of this command is suitable to be parsed by programs (plumbing) or only meant to be presented to humans (porcelain). For example, in some projects I am fetching commit SHA + author name + commit summary with this:

git log --pretty="%H%n%an%n%s" -1 HEAD

And then I split the output string by the newline character (I'm on Linux).

Besides, in some cases I also do something like this:

git log --pretty='[%h] %an: %s' -1 HEAD

And then parse the result with the following regex, expecting that a short SHA, the author name and the commit summary are in the captured groups:

^\[(\w+)\] ([^:]+): (.*)$

Is it a good approach? If not, what is the preferred way to programmatically get information about commits?

Answer 1

git log is a porcelain command.

It actually performs quite a disparate number of tasks — combining walking the revision graph, git diff and git grep and whatnot.

A plumbing way to do someting like

git log --pretty='[%h] %an: %s' -1 HEAD

is to combine git show-ref with git cat-file and parse the result—something like

git cat-file commit `git show-ref -s HEAD` |
  while read line; do
    # do some processing
  done

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Actually the root Git's manual page, git(1)—run git help git to read it—contains the breakdown of commands into porcelain and plumbing layers.