Regex Cheat Sheet

Regex cheat sheet with real commands and snippets for setup, core workflows, debugging, and production-safe automation patterns. If you are working across tools, pair this with the PHP Cheat Sheet and Ruby Cheat Sheet.

Setup and Validation

Goal: Run formatters and linters for content files

# Format project files when formatter is available
npx prettier -w . || true

# Lint Markdown/YAML/JSON if linters exist
npx markdownlint-cli2 '**/*.md' || npx yaml-language-server --help || true

# Search for TODO placeholders before publish
rg "TODO|TBD" .

Core Patterns

Goal: Use a production-safe snippet

# Match semantic version strings like 1.2.3
^v?(0|[1-9]\d*)\.(0|[1-9]\d*)\.(0|[1-9]\d*)(?:-[0-9A-Za-z.-]+)?$

# Match ISO date (YYYY-MM-DD)
^(19|20)\d\d-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01])$

# Capture domain from URL
^https?:\/\/(?:www\.)?([^\/]+)

Automation and CI

Goal: Add validation step to CI pipeline

# Run strict shell mode in CI
set -euo pipefail

# Validate syntax and formatting in one pass
npx prettier -c .

# Fail build if broken references exist
rg "](/[^)]+)" src/content -n

Debugging and Troubleshooting

Goal: Track parse failures quickly

# Use ripgrep to isolate malformed syntax
rg "{{|}}|<[^>]*$" src -n

# Print files with potential encoding issues
file -I src/content/sheets/*.md

# Re-run formatter with explicit parser
npx prettier --parser markdown src/content/sheets/*.md || true

Common Gotchas

• Keep Regex content valid and machine-readable for build pipelines.
• Avoid trailing commas or comments in strict JSON files.
• Use consistent heading depth to keep TOC generation stable.
• Prefer explicit encoding (UTF-8) for portability.
• Run formatter checks before committing content edits.

Related Sheets

• PHP Cheat Sheet — daily PHP commands and production-ready examples.
• Ruby Cheat Sheet — daily Ruby commands and production-ready examples.
• Rust Cheat Sheet — daily Rust commands and production-ready examples.