git-learn/skills/follow/references/env-detect.md

Environment Detection Rules

How to detect the runtime environment and guide the user through setup in /follow.

Language Detection from Config

Check these files in order. The first match is the primary language.

Config file	Language	Runtime check	Install command
package.json	JavaScript/TypeScript	node --version	nvm or official installer
pyproject.toml	Python	python --version	pyenv or python.org
go.mod	Go	go version	golang.org/dl
Cargo.toml	Rust	rustc --version	rustup
pom.xml	Java	java -version	SDKMAN or official
build.gradle / build.gradle.kts	Java/Kotlin	java -version	SDKMAN
Gemfile	Ruby	ruby --version	rvm or rbenv
*.csproj	C#/.NET	dotnet --version	.NET SDK
CMakeLists.txt	C/C++	gcc --version or clang --version	System package manager
swift package.json	Swift	swift --version	Xcode or swift.org

Dependency Installation

Once language is detected, guide the user:

JavaScript/TypeScript

# Check which package manager is used
if [ -f "yarn.lock" ]; then yarn install
elif [ -f "pnpm-lock.yaml" ]; then pnpm install
elif [ -f "bun.lockb" ] || [ -f "bun.lock" ]; then bun install
else npm install
fi

Python

# Modern Python projects
pip install -e .
# Or with requirements
pip install -r requirements.txt
# Or with poetry
poetry install
# Or with uv
uv pip install -r requirements.txt

Go

go mod download

Rust

cargo build

Java (Maven)

mvn install

Java (Gradle)

./gradlew build
# or
gradle build

Run Command Detection

How to start the project:

Source	Command
package.json → scripts.dev	npm run dev
package.json → scripts.start	npm start
Makefile → dev target	make dev
Makefile → run target	make run
pyproject.toml (Poetry)	poetry run python main.py
go.mod → package main	go run main.go
Cargo.toml → [[bin]]	cargo run
docker-compose.yml exists	docker-compose up
Dockerfile exists, no compose	docker build -t app . && docker run app

Common Environment Issues

Error	Cause	Fix
command not found: node	Node.js not installed	Install Node.js (recommend LTS)
ModuleNotFoundError	Python deps not installed	Run pip install -r requirements.txt
EACCES: permission denied	Global install without sudo	Use nvm/fnm, or prefix with sudo
ENOENT: no such file	Wrong working directory	cd to project root first
port already in use	Another process on same port	Kill the process or use different port
go: cannot find main module	Outside Go module	cd to directory with go.mod
error: could not find Cargo.toml	Outside Rust project	cd to directory with Cargo.toml
java.lang.UnsupportedClassVersionError	Wrong Java version	Match JDK version to project requirement
npm ERR! code ERESOLVE	Dependency conflict	Try npm install --legacy-peer-deps

Detection Script for /follow

# Quick environment check
echo "=== Environment ==="
node --version 2>/dev/null || echo "Node.js: not installed"
python --version 2>/dev/null || echo "Python: not installed"
go version 2>/dev/null || echo "Go: not installed"
rustc --version 2>/dev/null || echo "Rust: not installed"
java -version 2>/dev/null || echo "Java: not installed"
echo "PWD: $(pwd)"

Run this at the start of /follow Step 1 to understand what's available.