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+# nvm Copilot Instructions
+
+This document provides guidance for GitHub Copilot when working with the Node Version Manager (nvm) codebase.
+
+## Overview
+
+nvm is a version manager for Node.js, implemented as a POSIX-compliant function that works across multiple shells (sh, dash, bash, ksh, zsh). The codebase is primarily written in shell script and emphasizes portability and compatibility.
+
+### Core Architecture
+
+- **Main script**: `nvm.sh` - Contains all core functionality and the main `nvm()` function
+- **Installation script**: `install.sh` - Handles downloading and installing nvm itself
+- **Execution wrapper**: `nvm-exec` - Allows running commands with specific Node.js versions
+- **Bash completion**: `bash_completion` - Provides tab completion for bash users
+- **Tests**: Comprehensive test suite in `test/` directory using the urchin test framework
+
+## Key Files and Their Purposes
+
+### `nvm.sh`
+The core functionality file containing:
+- Main `nvm()` function (starts around line 3000)
+- All internal helper functions (prefixed with `nvm_`)
+- Command implementations for install, use, ls, etc.
+- Shell compatibility logic
+- POSIX compliance utilities
+
+### `install.sh`
+Handles nvm installation via curl/wget:
+- Downloads nvm from GitHub
+- Sets up directory structure
+- Configures shell integration
+- Supports both git clone and script download methods
+
+### `nvm-exec`
+Simple wrapper script that:
+- Sources nvm.sh with `--no-use` flag
+- Switches to specified Node version via `NODE_VERSION` env var or `.nvmrc`
+- Executes the provided command with that Node version
+
+## Top-Level nvm Commands and Internal Functions
+
+### Core Commands
+
+#### `nvm install [version]`
+- **Internal functions**: `nvm_install_binary()`, `nvm_install_source()`, `nvm_download_artifact()`
+- Downloads and installs specified Node.js version
+- Supports LTS versions, version ranges, and aliases
+- Can install from binary or compile from source
+
+#### `nvm use [version]`
+- **Internal functions**: `nvm_resolve_alias()`, `nvm_version_path()`, `nvm_change_path()`
+- Switches current shell to use specified Node.js version
+- Updates PATH environment variable
+- Supports `.nvmrc` file integration
+
+#### `nvm ls [pattern]`
+- **Internal functions**: `nvm_ls()`, `nvm_tree_contains_path()`
+- Lists installed Node.js versions
+- Supports pattern matching and filtering
+- Shows current version and aliases
+
+#### `nvm ls-remote [pattern]`
+- **Internal functions**: `nvm_ls_remote()`, `nvm_download()`, `nvm_ls_remote_index_tab()`
+- Lists available Node.js versions from nodejs.org
+- Supports LTS filtering and pattern matching
+- Downloads version index on-demand
+
+#### `nvm alias [name] [version]`
+- **Internal functions**: `nvm_alias()`, `nvm_alias_path()`
+- Creates symbolic links for version aliases
+- Special aliases: `default`, `node`, `stable`, `unstable`
+- Stored in `$NVM_DIR/alias/` directory
+
+#### `nvm current`
+- **Internal functions**: `nvm_ls_current()`
+- Shows currently active Node.js version
+- Returns "system" if using system Node.js
+
+#### `nvm which [version]`
+- **Internal functions**: `nvm_version_path()`, `nvm_resolve_alias()`
+- Shows path to specified Node.js version
+- Resolves aliases and version strings
+
+### Utility Commands
+
+#### `nvm cache clear|dir`
+- Cache management for downloaded binaries
+- Clears or shows cache directory path
+
+#### `nvm debug`
+- Diagnostic information for troubleshooting
+- Shows environment, tool versions, and paths
+
+#### `nvm deactivate`
+- Removes nvm modifications from current shell
+- Restores original PATH
+
+#### `nvm unload`
+- Completely removes nvm from shell environment
+- Unsets all nvm functions and variables
+
+### Internal Function Categories
+
+#### Version Resolution
+- `nvm_resolve_alias()` - Resolves aliases to version numbers
+- `nvm_version()` - Finds best matching local version
+- `nvm_remote_version()` - Finds best matching remote version
+- `nvm_normalize_version()` - Standardizes version strings
+
+#### Installation Helpers
+- `nvm_install_binary()` - Downloads and installs precompiled binaries
+- `nvm_install_source()` - Compiles Node.js from source
+- `nvm_download_artifact()` - Downloads tarballs or binaries
+- `nvm_compute_checksum()` - Verifies download integrity
+
+#### Path Management
+- `nvm_change_path()` - Updates PATH for version switching
+- `nvm_strip_path()` - Removes nvm paths from PATH
+- `nvm_version_path()` - Gets installation path for version
+
+#### Utility Functions
+- `nvm_echo()`, `nvm_err()` - Output functions
+- `nvm_has()` - Checks if command exists
+- `nvm_is_zsh()` - Shell detection
+- `nvm_sanitize_path()` - Cleans sensitive data from paths
+
+## Running Tests
+
+### Test Framework
+nvm uses the **urchin** test framework for shell script testing.
+
+### Test Structure
+```
+test/
+├── fast/           # Quick unit tests
+├── slow/           # Integration tests
+├── sourcing/       # Shell sourcing tests
+├── install_script/ # Installation script tests
+├── installation_node/ # Node installation tests
+└── common.sh       # Shared test utilities
+```
+
+### Running Tests
+
+#### Install Dependencies
+```bash
+npm install  # Installs urchin, semver, and replace tools
+```
+
+#### Run All Tests
+```bash
+npm test               # Runs tests in current shell
+make test              # Runs tests in all supported shells
+make test-bash         # Runs tests only in bash
+make test-zsh          # Runs tests only in zsh
+```
+
+#### Run Specific Test Suites
+```bash
+make TEST_SUITE=fast test        # Only fast tests
+make TEST_SUITE=slow test        # Only slow tests
+make SHELLS=bash test            # Only bash shell
+```
+
+#### Individual Test Execution
+```bash
+./test/fast/Unit\ tests/nvm_get_arch     # Run single test
+urchin test/fast/                        # Run fast test suite
+```
+
+### Test Writing Guidelines
+- Tests should work across all supported shells (sh, bash, dash, zsh)
+- Use `die()` function for test failures
+- Clean up after tests in cleanup functions
+- Mock external dependencies when needed
+- Place mocks in `test/mocks/` directory
+
+## Shell Environment Setup
+
+### Supported Shells
+- **bash** - Full feature support
+- **zsh** - Full feature support  
+- **dash** - Basic POSIX support
+- **sh** - Basic POSIX support
+- **ksh** - Limited support (experimental)
+
+### Installing Shell Environments
+
+#### Ubuntu/Debian
+```bash
+sudo apt-get update
+sudo apt-get install bash zsh dash ksh
+```
+
+#### macOS
+```bash
+# zsh is default, install others via Homebrew
+brew install bash dash ksh
+```
+
+#### Manual Shell Testing
+```bash
+# Test in specific shell
+bash -c "source nvm.sh && nvm --version"
+zsh -c "source nvm.sh && nvm --version"
+dash -c ". nvm.sh && nvm --version"
+```
+
+### Shell-Specific Considerations
+- **zsh**: Requires `setopt local_options shwordsplit` for word splitting
+- **dash**: Limited feature set, avoid bash-specific syntax
+- **ksh**: Some features may not work, primarily for compatibility testing
+
+## CI Environment Details
+
+### GitHub Actions Workflows
+
+#### `.github/workflows/tests.yml`
+- Runs test suite across multiple shells and test suites
+- Uses `script` command for proper TTY simulation
+- Matrix strategy covers shell × test suite combinations
+- Excludes install_script tests from non-bash shells
+
+#### `.github/workflows/shellcheck.yml`
+- Lints all shell scripts using shellcheck
+- Tests against multiple shell targets (bash, sh, dash, ksh)
+- Uses Homebrew to install latest shellcheck version
+
+#### `.github/workflows/lint.yml`
+- Runs additional linting and formatting checks
+- Validates documentation and code style
+
+### Travis CI (Legacy)
+- Configured in `.travis.yml`
+- Tests on multiple Ubuntu versions
+- Installs shell environments via apt packages
+
+### CI Test Execution
+```bash
+# Simulate CI environment locally
+export TRAVIS_BUILD_DIR=""  # Disable Travis-specific logic
+export GITHUB_ACTIONS=""    # Disable GitHub Actions logic
+make test
+```
+
+## Setting Up shellcheck Locally
+
+### Installation
+
+#### macOS (Homebrew)
+```bash
+brew install shellcheck
+```
+
+#### Ubuntu/Debian
+```bash
+sudo apt-get install shellcheck
+```
+
+#### From Source
+```bash
+# Download from https://github.com/koalaman/shellcheck/releases
+wget https://github.com/koalaman/shellcheck/releases/download/latest/shellcheck-latest.linux.x86_64.tar.xz
+tar -xf shellcheck-latest.linux.x86_64.tar.xz
+sudo cp shellcheck-latest/shellcheck /usr/local/bin/
+```
+
+### Usage
+
+#### Lint Main Files
+```bash
+shellcheck -s bash nvm.sh
+shellcheck -s bash install.sh  
+shellcheck -s bash nvm-exec
+shellcheck -s bash bash_completion
+```
+
+#### Lint Across Shell Types
+```bash
+shellcheck -s sh nvm.sh      # POSIX sh
+shellcheck -s bash nvm.sh    # Bash extensions
+shellcheck -s dash nvm.sh    # Dash compatibility
+shellcheck -s ksh nvm.sh     # Ksh compatibility
+```
+
+#### Common shellcheck Directives in nvm
+- `# shellcheck disable=SC2039` - Allow bash extensions in POSIX mode
+- `# shellcheck disable=SC2016` - Allow literal `$` in single quotes
+- `# shellcheck disable=SC2001` - Allow sed usage instead of parameter expansion
+- `# shellcheck disable=SC3043` - Allow `local` keyword (bash extension)
+
+### Fixing shellcheck Issues
+1. **Quoting**: Always quote variables: `"${VAR}"` instead of `$VAR`
+2. **POSIX compliance**: Avoid bash-specific features in portable sections
+3. **Array usage**: Use `set --` for positional parameters instead of arrays
+4. **Local variables**: Mark as bash-specific or avoid in POSIX functions
+
+## Development Best Practices
+
+### Code Style
+- Use 2-space indentation
+- Follow POSIX shell guidelines for portability
+- Prefix internal functions with `nvm_`
+- Use `nvm_echo` instead of `echo` for output
+- Use `nvm_err` for error messages
+
+### Compatibility
+- Test changes across all supported shells
+- Avoid bash-specific features in core functionality
+- Use `nvm_is_zsh` checks when zsh-specific behavior needed
+- Mock external dependencies in tests
+
+### Performance
+- Cache expensive operations (like remote version lists)
+- Use local variables to avoid scope pollution
+- Minimize subprocess calls where possible
+- Implement lazy loading for optional features
+
+### Debugging
+- Use `nvm debug` command for environment information
+- Enable verbose output with `set -x` during development
+- Test with `NVM_DEBUG=1` environment variable
+- Check `$NVM_DIR/.cache` for cached data issues
+
+## Common Gotchas
+
+1. **PATH modification**: nvm modifies PATH extensively; be careful with restoration
+2. **Shell sourcing**: nvm must be sourced, not executed as a script
+3. **Version resolution**: Aliases, partial versions, and special keywords interact complexly
+4. **Platform differences**: Handle differences between Linux, macOS, and other Unix systems
+5. **Network dependencies**: Many operations require internet access for version lists
+6. **Concurrent access**: Multiple shells can conflict when installing versions simultaneously
+
+This guide should help GitHub Copilot understand the nvm codebase structure, testing procedures, and development environment setup requirements.
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