shell-expert

# Shell Expert Expert knowledge for shell scripting, command-line tools, and automation with focus on robust, portable, and efficient solutions. ## When to Use This Skill | Use this skill when... | Use justfile-expert instead when... | |---|---| | Authoring portable bash, zsh, or POSIX shell scripts | Wrapping commands as named recipes for a project task runner | | Composing pipelines and one-off automation logic | Standardising entry points across a team or repo | | Hardening scripts with `set -euo pipefail`, traps, and quoting | Defining cross-platform commands without writing shell glue | | Use this skill when... | Use jq-json-processing instead when... | |---|---| | Glue logic that wires together CLI tools | The work is purely transforming JSON input | | Writing reusable functions, argument parsing, or signal handling | A single jq expression can replace a chain of shell commands | **Command-Line Tool Mastery** - Expert knowledge of modern CLI tools (jq, yq, fd, rg, etc.) - JSON/YAML processing and transformation - File searching and text manipulation - System automation and orchestration **Shell Scripting Excellence** - POSIX-compliant shell scripting for maximum portability - Bash-specific features and best practices - Error handling and defensive programming - Cross-platform compatibility (Linux, macOS, BSD) **Automation & Integration** - CI/CD pipeline scripting - System administration automation - Tool integration and workflow automation - Performance optimization for shell operations ## Key Capabilities **JSON/YAML Processing** - **jq**: Complex JSON queries, transformations, and filtering - **yq**: YAML manipulation, in-place editing, format conversion - **jd**: JSON diffing and patching for configuration management - **Data pipeline construction**: Chaining tools for complex transformations **File Operations & Search** - **fd**: Fast, user-friendly file finding with intuitive syntax - **rg (ripgrep)**: Lightning-fast recursive grep with gitignore support - **lsd**: Modern ls replacement with visual enhancements - **find/grep alternatives**: When and how to use modern replacements **Shell Script Development** - **Error Handling**: Proper trap usage, exit codes, error propagation - **Input Validation**: Argument parsing, option handling, user input sanitization - **Debugging**: Set options (-x, -e, -u, -o pipefail), debug output strategies - **Performance**: Process substitution, parallel execution, efficient loops **Cross-Platform Scripting** - **Platform Detection**: OS-specific behavior handling - **Path Management**: Portable path construction and manipulation - **Tool Availability**: Checking for and handling missing dependencies - **Compatibility Layers**: Writing scripts that work everywhere **Automation Patterns** - **Idempotent Operations**: Scripts that can run multiple times safely - **Atomic Operations**: Ensuring all-or-nothing execution - **Progress Reporting**: User-friendly output and status updates - **Logging & Monitoring**: Structured logging for automated systems ## Essential Commands **jq - JSON Processing** ```bash jq . data.json # Pretty-print jq -r '.key.subkey' data.json # Extract value jq '.items[] | select(.status == "active")' # Filter ``` **yq - YAML Processing** ```bash yq '.services.web.image' docker-compose.yml # Read value yq -i '.version = "2.1.0"' config.yml # Update in-place yq -o json config.yml # Convert to JSON ``` **fd - Fast File Finding** ```bash fd 'pattern' # Find by pattern fd -e md # Find by extension fd -e sh -x shellcheck {} # Find and execute ``` **rg - Recursive Grep** ```bash rg 'DATABASE_URL' # Basic search rg 'TODO' -t python # Search specific file types rg -C 3 'error' # Search with context ``` ## Best Practices **Script Development Workflow** 1. **Requirements Analysis**: Understand automation need and target platforms 2. **Tool Selection**: Choose appropriate tools for the task 3. **Prototype Development**: Create initial script with core functionality 4. **Error Handling**: Add robust error handling and edge case management 5. **Cross-Platform Testing**: Verify script works on all target systems 6. **Performance Optimization**: Profile and optimize for efficiency 7. **Documentation**: Add clear usage instructions and inline comments **Critical Guidelines** - Always use shellcheck for linting - Set strict mode: `set -euo pipefail` - Quote all variables: `"${var}"` - Use functions for reusable code - Implement proper cleanup with trap - Provide helpful error messages - Include --help and --version options - Use meaningful variable names - Comment complex logic - Test with different shells when targeting POSIX ## Common Patterns **Robust Script Template** ```bash #!/usr/bin/env bash set -euo pipefail IFS=$'\n\t' trap 'echo "Error on line $LINENO"' ERR trap cleanup EXIT cleanup() { rm -f "$TEMP_FILE" 2>/dev/null || true } main() { parse_args "$@" validate_environment execute_task } main "$@" ``` **Cross-Platform Detection** ```bash detect_os() { case "$OSTYPE" in linux*) OS="linux" ;; darwin*) OS="macos" ;; msys*) OS="windows" ;; *) OS="unknown" ;; esac } ``` For detailed command-line tools reference, advanced automation examples, and troubleshooting guidance, see REFERENCE.md.