Regular Expressions for Beginners: 20 Handy Patterns and Four Debugging Tricks
WebTool Team · Published 2026-09-04 · Regular Expressions / Regex / Development
A regular expression describes string-matching rules with a compact notation — about 10 metacharacters cover 80% of everyday needs. As you write a pattern, validate it live in our regex tester, which offers real-time highlighting and group extraction.
Metacharacter cheat sheet
| Symbol | Meaning | Example |
|---|---|---|
. |
Any character (except newline) | a.c matches abc |
\d \w \s |
Digit / word character / whitespace | \d{4} matches a year |
[abc] [^abc] |
Character set / negation | [0-9a-f] hexadecimal |
* + ? |
0+ / 1+ / 0 or 1 times | colou?r |
{n,m} |
n to m times | \d{6} postal code |
^ $ |
Start / end of line | ^# matches heading lines |
() |
Group (capturing) | (\d+)-(\d+) |
(?:) |
Non-capturing group | (?:https?://) |
| ` | ` | Alternation |
20 handy patterns
| Use case | Pattern |
|---|---|
| Mainland China mobile number | ^1[3-9]\d{9}$ |
| Email (lenient) | ^[\w.+-]+@[\w-]+\.[\w.]+$ |
| URL | ^https?://[\w.-]+(?::\d+)?(?:/\S*)?$ |
| IPv4 | `^((25[0-5] |
| Date YYYY-MM-DD | `^\d{4}-(0[1-9] |
| Chinese name | ^[一-龥]{2,4}$ |
| Chinese national ID (18 digits) | ^\d{17}[\dXx]$ |
| Strong password (8+ chars, upper/lower/digit) | ^(?=.*[a-z])(?=.*[A-Z])(?=.*\d).{8,}$ |
| Extract HTML tag contents | <([a-z]+)[^>]*>(.*?)</\1> |
| Blank lines | ^\s*$ |
| Hex color | ^#(?:[0-9a-fA-F]{3}){1,2}$ |
| Base64 | ^[A-Za-z0-9+/]+={0,2}$ |
| Chinese punctuation | [，。！？；：""''（）] |
| Thousands-separated numbers | \d{1,3}(?:,\d{3})+ |
| Version number | ^\d+\.\d+\.\d+$ |
| File extension | \.([a-z0-9]+)$ |
| camelCase to words | ([a-z])([A-Z]) → $1 $2 |
| Trailing whitespace | [ \t]+$ |
| Repeated characters | (.)\1{2,} |
| Comment lines (//) | ^\s*//.*$ |
Four debugging tricks
- Greedy vs. lazy:
.*consumes up to the last possible match, while.*?stops at the first. For quoted content,"[^"]*"is safer than".*". - Catastrophic backtracking (ReDoS): nested quantifiers like
(a+)+backtrack exponentially on hostile input — enforce an input length limit in online services. - Don't forget anchors: add
^...$to validate an entire string, otherwise\d+happily matches inside "abc123". - Escaping layers: when writing regex inside string literals (Java/Python),
\dmust be written as"\\d"— raw strings (Pythonr"") avoid this.
Last updated: 2026-09-04