Negative Integer Validation Regex

Validate negative integers (negative whole numbers) using a simple regex pattern with minus sign.

Pattern Breakdown

^-\d+$

Components

Character Classes

• - - Literal minus sign
• \d - Any digit (0-9)
• + - Quantifier: one or more occurrences

Examples

Valid:

• -1
• -123
• -999999
• -1000000

Invalid:

• 0 (zero is not negative)
• 5 (positive number)
• -0 (negative zero, typically not considered negative)
• --5 (double minus)
• -12.5 (decimal)
• -abc (non-numeric)

Implementation

JavaScript

const negativeIntRegex = /^-\d+$/;
negativeIntRegex.test('-123'); // true
negativeIntRegex.test('-1'); // true
negativeIntRegex.test('5'); // false (positive)
negativeIntRegex.test('-12.5'); // false (decimal)
negativeIntRegex.test('0'); // false (zero)

Python

import re
negative_int_regex = r'^-\d+$'
bool(re.match(negative_int_regex, '-123'))  # True
bool(re.match(negative_int_regex, '-1'))  # True
bool(re.match(negative_int_regex, '5'))  # False (positive)
bool(re.match(negative_int_regex, '-12.5'))  # False (decimal)

Go

negativeIntRegex := regexp.MustCompile(`^-\d+$`)
negativeIntRegex.MatchString("-123") // true
negativeIntRegex.MatchString("-1") // true
negativeIntRegex.MatchString("5") // false (positive)
negativeIntRegex.MatchString("-12.5") // false (decimal)

Limitations

1. Includes -0: Matches -0 (may want to exclude this)
2. No size limit: Doesn't enforce maximum/minimum value
3. String validation: Validates string format, not actual integer type
4. No leading zeros: Accepts -0123 (may want to prevent this)
5. No scientific notation: Doesn't support -1e5 format

When to Use

• Negative integer input validation
• Temperature below zero
• Debt/credit calculations
• When you need to ensure negative numbers only
• Form input validation for negative values

For production, consider:

• Excluding -0 if needed: ^-(0*[1-9]\d*)$
• Preventing leading zeros: ^-(0|[1-9]\d*)$
• Adding value range validation
• Converting to integer type after validation
• Handling edge cases for very large negative numbers