VCS Detection Skill

Detect the version control system in use before running VCS commands.

Why This Matters

• jj and git have different CLIs and workflows.
• Running git commands in a jj repo (or vice versa) causes avoidable errors.
• Some repos are colocated (both .jj/ and .git/ exist).

Detection Logic

Priority order:

1. jj root succeeds -> jj
2. else git rev-parse --show-toplevel succeeds -> git
3. else -> none

Detection Command

if jj root &>/dev/null; then echo "jj"
elif git rev-parse --show-toplevel &>/dev/null; then echo "git"
else echo "none"
fi

Common Command Mapping

Operation	git	jj
Status	git status	jj status
Log	git log	jj log
Diff	git diff	jj diff
Commit	git commit	jj commit / jj describe
Branch list	git branch	jj branch list
New branch	git checkout -b <name>	jj branch create <name>
Push	git push	jj git push
Fetch/Pull	git fetch / git pull	jj git fetch
Rebase	git rebase	jj rebase

Usage

Before VCS operations:

1. Run the detection command.
2. Use the matching CLI (jj or git).
3. If none, report that the directory is not version controlled.

Colocated Repos

If both .jj/ and .git/ exist, prefer jj commands and use git compatibility subcommands when needed.