RegexSandbox
Test regular expressions, inspect captured groups in real-time, and reference exhaustive regex token cheatsheets.
Google Cloud • AI & Developer Infrastructure
Regular Expressions (RegExp) Syntax & Match Group Reference
Regular expressions (regex) are sequences of characters defining search patterns, extensively used in input validation, text scraping, lexical tokenization, and string transformations. DevCraft matches regex patterns using JavaScript's native RegExp virtual machine directly in local memory.
How It Works (In-Memory Execution)
- Pattern Compilation: The pattern string and modifier flags (g, i, m, s) are compiled into a native JavaScript RegExp object.
- Iterative Lexical Matching: For global flags (g), RegExp.exec is executed iteratively to record character index offsets, match strings, and captured groups.
- Capture Group Extraction: Parenthesized expressions are segmented into discrete capturing subgroups indexed from 1 to N.
Core Regular Expression Syntax Cheatsheet
| Parameter / Token | Description | Example |
|---|---|---|
| \d / \D | Matches any digit (0-9) / matches any non-digit character. | \d{4} |
| \w / \W | Matches any word character (letters, digits, underscore) / non-word. | \w+ |
| ^ and $ | Anchor at the start of a string / anchor at the end of a string. | ^https: |
| (?:...) | Non-capturing group (groups characters without saving a numbered group). | (?:https|http) |
| (?=...) / (?!...) | Positive lookahead / negative lookahead assertion. | \d+(?=px) |
Frequently Asked Questions
Q: What does the 'g' flag do in regular expressions?
The 'g' (global) flag instructs the regex engine to continue searching across the entire input string rather than halting at the first match.
Q: What does the 'i' flag do?
The 'i' (ignoreCase) flag causes the search to be case-insensitive, treating uppercase and lowercase letters as identical.
Q: Is RegexSandbox safe from catastrophic backtracking (ReDoS)?
DevCraft runs regex matches locally in your browser with execution limits to prevent browser freezing, ensuring complete isolation from external server threats.