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Write and Explain a Regex With Test Cases

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The prompt

Write a regular expression for me and prove it works. What it should match: [e.g. Indian mobile numbers with or without +91 / PAN format / dates like 17-10-2026 / email addresses in a log line] What it must NOT match: [examples] Where I'll use it: [Python / JavaScript / Java / grep / a form validator / Excel or Google Sheets] Whole-string match or find inside text: [ ] Give me: 1. The regex, written for my language's flavour. 2. A piece-by-piece explanation in a table: part | meaning. 3. Ten test strings: six that should match and four that shouldn't, including tricky edge cases, with the expected result for each. 4. A tiny code snippet that runs those tests in my language. 5. Limits: what the pattern deliberately doesn't check (e.g. it validates format, not whether the number exists). Rules: prefer a readable pattern over a clever one; avoid patterns that can backtrack badly on long input; if my examples conflict, point that out first.

Why this prompt

• Hand-picked, editorially reviewed prompt
• Written for ChatGPT, Claude, Gemini

Source

Created by BestPromptFinder — editorial prompt, not user-generated. See our content & source policy.

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