regex-builder

Original：🇺🇸 English

Translated

Build, test, and explain regular expressions against sample text or files using CLI tools (rg, python) and specific regex flavors. Use when asked to craft, debug, or validate regexes or search patterns.

17installs

Sourcejmerta/codex-skills

Added on2026-04-03

NPX Install

npx skill4agent add jmerta/codex-skills regex-builder

SKILL.md Content

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Regex builder

Goal

Produce a correct, testable regex with rationale and runnable verification.

Inputs to confirm (ask if missing)

Target regex flavor/engine (PCRE, Python, JavaScript, .NET, RE2, etc.).
Example matches and non-matches (at least 3 each when possible).
Scope: single-line vs multi-line; file types/paths.
Output needs: capture groups, named groups, replacement template.

Workflow

Gather samples
- Ask for sample text or identify files.
- If files exist, locate with
```
rg --files
```
  and preview with
```
rg -n
```
  .
Choose tool
- Prefer
```
rg
```
  for quick match checks; use
```
rg -P
```
  for PCRE features.
- Use Python for detailed group inspection when needed.
Build incrementally
- Start with a minimal literal anchor; expand piece by piece.
- Add anchors/boundaries; handle whitespace and separators explicitly.
Validate
- Show a command to test against samples.
- Confirm no false positives by testing non-matches.
Deliver
- Provide final regex, flags, and explanation.
- Include a test command and expected match summary.
- Note any tradeoffs/backtracking risks.

CLI snippets (use as needed)

Ripgrep check:

```
rg -n "<regex>" path\\to\\file
```
```
rg -n -P "<regex>" path\\to\\file
```

Python quick test (adjust quoting for the shell):

python -c "import re,sys;pat=re.compile(r'<regex>');data=sys.stdin.read();print([m.group(0) for m in pat.finditer(data)])" < path\\to\\file

Deliverables

Regex + flags and any capture group map.
Test command(s) and summary of matches/non-matches.
Short explanation of the approach and known limitations.