Add Determine Absolute Path Of Top-Level Project Directory as a Git TIL

git/determine-absolute-path-of-top-level-project-directory.md

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+# Determine Absolute Path Of Top-Level Project Directory
+
+The `git rev-parse` command is a git plumbing command for parsing different
+kinds of things in git into a canonical form that can be used in a deterministic
+way by scripts. I would typically think of using it to work with branch names,
+tags, and other kinds of refs.
+
+There is a handy, sorta off-label use for it in determining the absolute path of
+the root directory for the current git repository. Use the `--show-toplevel`
+flag with no other arguments.
+
+```bash
+❯ git rev-parse --show-toplevel
+/Users/lastword/dev/jbranchaud/til
+```
+
+Here, I am in the local copy of [my TIL repo](https://github.com/jbranchaud/til). This command gives me the absolute
+path of the top-level directory where that `.git` directory resides.
+
+This is useful for scripts that need to orient themselves to the current
+project's top-level directory regardless of what directory they are being
+executed from. This is useful for things like a git hook script or monorepos
+with scripts located in a specific sub-project directory.
+
+Also worth mentioning is the `--show-superproject-working-tree` flag. In my TIL
+repo, I have a private repository included as a submodule. Within that directory
+`--show-toplevel` will produce the absolute path to the submodule. If I instead
+want the absolute path of the _super project_ (in this case TIL), then I can use
+this other flag.
+
+```bash
+❯ git rev-parse --show-toplevel
+/Users/lastword/dev/jbranchaud/til/notes
+
+❯ git rev-parse --show-superproject-working-tree
+/Users/lastword/dev/jbranchaud/til
+```
+
+See `man git-rev-parse` for more details.