Comprehensive Regular Expression Cheat Sheet for Common Validation Scenarios

1. Numeric Validation Expressions

Digits: ^[0-9]*$

Exact n digits: ^\d{n}$

At least n digits: ^\d{n,}$

m‑n digits: ^\d{m,n}$

Zero or non‑zero leading numbers: ^(0|[1-9][0-9]*)$

Non‑zero start with up to two decimal places: ^([1-9][0-9]*)+(.[0-9]{1,2})?$

Positive/negative numbers with optional 1‑2 decimal places: ^(\-)?\d+(\.\d{1,2})?$

Positive, negative or decimal: ^(\-|\+)?\d+(\.\d+)?$

Positive real number with two decimal places: ^[0-9]+(.[0-9]{2})?$

Positive real number with 1‑3 decimal places: ^[0-9]+(.[0-9]{1,3})?$

Non‑zero positive integer: ^[1-9]\d*$ or ^([1-9][0-9]*){1,3}$ or ^\+?[1-9][0-9]*$

Non‑zero negative integer: ^-?[1-9]\d*$

Non‑negative integer: ^\d+$ or ^[1-9]\d*|0$

Non‑positive integer: ^-?[1-9]\d*|0$ or (^(-\d+)|(0+))$

Non‑negative floating point: ^\d+(\.\d+)?$ or more complex version ^[1-9]\d*\.\d*|0\.\d*[1-9]\d*|0?\.0+|0$

Non‑positive floating point: ^((-\d+(\.\d+)?)|(0+(\.0+)?))$ or ^(-([1-9]\d*\.\d*|0\.\d*[1-9]\d*))|0?\.0+|0$

Positive floating point: ^[1-9]\d*\.\d*|0\.\d*[1-9]\d*$ or a combined pattern handling integers as well.

Negative floating point: ^-([1-9]\d*\.\d*|0\.\d*[1-9]\d*)$

General floating point (optional sign): ^(-?\d+)(\.\d+)?$ or ^-?([1-9]\d*\.\d*|0\.\d*[1-9]\d*|0?\.0+|0)$

2. Character Validation Expressions

Chinese characters: ^[\u4e00-\u9fa5]{0,}$

Alphanumeric (A‑Z, a‑z, 0‑9): ^[A-Za-z0-9]+$ or length‑restricted ^[A-Za-z0-9]{4,40}$

Any characters length 3‑20: ^.{3,20}$

Only letters: ^[A-Za-z]+$

Only uppercase letters: ^[A-Z]+$

Only lowercase letters: ^[a-z]+$

Alphanumeric only: ^[A-Za-z0-9]+$

Alphanumeric with underscore: ^\w+$ or length‑restricted ^\w{3,20}

Chinese, English, digits, underscore: ^[\u4E00-\u9FA5A-Za-z0-9_]+$

Chinese, English, digits (no underscore): ^[\u4E00-\u9FA5A-Za-z0-9]+$ or ^[\u4E00-\u9FA5A-Za-z0-9]{2,20}$

Allow specific punctuation: ^[%&',;=?$\"]+$ and exclude them with [^%&',;=?$\x22]+

Disallow tilde: [^~\x22]+

3. Special‑Requirement Expressions

Email address: ^\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*$

Domain name: [a-zA-Z0-9][-a-zA-Z0-9]{0,62}(/.[a-zA-Z0-9][-a-zA-Z0-9]{0,62})+/.?

Internet URL: [a-zA-z]+://[^\s]* or ^http://([\w-]+\.)+[\w-]+(/[\w-./?%&=]*)?$

Mobile phone number (China): ^(13[0-9]|14[5|7]|15[0-9]|18[0-9])\d{8}$

Telephone numbers (various formats): ^(\(\d{3,4}-)|\d{3.4}-)?\d{7,8}$

Domestic telephone (e.g., 0511‑4405222): \d{3}-\d{8}|\d{4}-\d{7}

Identity card (15 or 18 digits): ^\d{15}|\d{18}$

Short ID (digits, optional trailing x): ^([0-9]){7,18}(x|X)?$ or ^\d{8,18}|[0-9x]{8,18}|[0-9X]{8,18}?$

Username (letter start, 5‑16 chars, letters/digits/underscore): ^[a-zA-Z][a-zA-Z0-9_]{4,15}$

Password (letter start, 6‑18 chars, letters/digits/underscore): ^[a-zA-Z]\w{5,17}$

Strong password (8‑10 chars, must contain upper, lower, digit, no special chars): ^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).{8,10}$

Date format (yyyy‑mm‑dd): ^\d{4}-\d{1,2}-\d{1,2}

Month (01‑12): ^(0?[1-9]|1[0-2])$

Day of month (01‑31): ^((0?[1-9])|((1|2)[0-9])|30|31)$

4. Additional Useful Regular Expressions

Money formats (various examples): ^[1-9][0-9]*$ , ^(0|[1-9][0-9]*)$ , ^(0|-?[1-9][0-9]*)$ , ^[0-9]+(.[0-9]+)?$ , ^[0-9]+(.[0-9]{2})?$ , ^[0-9]+(.[0-9]{1,2})?$ , ^[0-9]{1,3}(,[0-9]{3})*(.[0-9]{1,2})?$ , ^([0-9]+|[0-9]{1,3}(,[0-9]{3})*)(.[0-9]{1,2})?$

XML file name: ^([a-zA-Z]+-?)+[a-zA-Z0-9]+\.[xX][mM][lL]$

Chinese character regex: [\u4e00-\u9fa5]

Double‑byte characters: [^\x00-\xff]

Blank line removal: \n\s*\r

HTML tag extraction: <(\S*?)[^>]*>.*?</\1>|<.*? />

Leading/trailing whitespace: ^\s*|\s*$ or (^\s*)|(\s*$)

QQ number (>=10000): [1-9][0-9]{4,}

Chinese postal code: [1-9]\d{5}(?!\d)

IPv4 address simple: \d+\.\d+\.\d+\.\d+

IPv4 address strict: ((?:(?:25[0-5]|2[0-4]\d|[01]?\d?\d)\.){3}(?:25[0-5]|2[0-4]\d|[01]?\d?\d))

IPv6 address: (([0-9a-fA-F]{1,4}:){7,7}[0-9a-fA-F]{1,4}|...|::(ffff(:0{1,4}){0,1}:){0,1}((25[0-5]|...)))

Subnet mask: same pattern as IPv4 above.

Date validation with leap year support: ^(?:(?!0000)[0-9]{4}-(?:(?:0[1-9]|1[0-2])-(?:0[1-9]|1[0-9]|2[0-8])|(?:0[13-9]|1[0-2])-(?:29|30)|(?:0[13578]|1[02])-31)|(?:[0-9]{2}(?:0[48]|[2468][048]|[13579][26])|(?:0[48]|[2468][048]|[13579][26])00)-02-29)$

Comment extraction: <!--(.*?)-->

CSS property detection: ^\s*[a-zA-Z\-]+\s*[:]{1}\s[a-zA-Z0-9\s.#]+[;]{1}

HTML link extraction (complex example): (<a\s*(?!.*\brel=)[^>]*)(href="https?:\/\/)((?!(?:(?:www\.)?'.implode('|(?:www\.)?', $follow_list).'))[^" rel="external nofollow" ]+)("...)

Image source extraction: \< *[img][^\\>]*[src] *= *[\"\']{0,1}([^\"\'\ >]*)

Hex colour code: ^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$

File extension validation (example for .txt): ^([a-zA-Z]\:|\\)\\([^\\]+\\)*[^\/:*?"<>|]+\.txt(l)?$

IE version detection: ^.*MSIE [5-8](?:\.[0-9]+)?(?!.*Trident\/[5-9]\.0).*$