Go (RE2)

JSON Number (Strict) in GO

Match JSON-spec numbers — disallows leading zeros (no `01`), allows decimals and exponents.

Try it in the GO tester →

Pattern

regexGO
-?(?:0|[1-9]\d*)(?:\.\d+)?(?:[eE][-+]?\d+)?   (flags: g)

Go (RE2) code

goGo
package main

import (
	"fmt"
	"regexp"
)

func main() {
	re := regexp.MustCompile(`-?(?:0|[1-9]\d*)(?:\.\d+)?(?:[eE][-+]?\d+)?`)
	input := `values: 0, 42, -3.14, 6.022e23`
	for _, match := range re.FindAllString(input, -1) {
		fmt.Println(match)
	}
}

Uses `regexp.MustCompile` (panics on bad patterns at startup) and `FindAllString` for all matches.

How the pattern works

-? optional sign. (?:0|[1-9]\d*) the integer part: either a single zero or a non-zero digit followed by any digits (no leading zeros allowed per RFC 8259). (?:\.\d+)? optional decimal part. (?:[eE][-+]?\d+)? optional exponent. Strict per JSON spec — won't match `01` or `1.` (which are valid JS but not JSON).

Examples

Input

values: 0, 42, -3.14, 6.022e23

Matches

  • 0
  • 42
  • -3.14
  • 6.022e23

Input

0.5 vs invalid 01

Matches

  • 0.5
  • 0
  • 1

Input

no numbers

No match

—

Same pattern, other engines

JavaScript / ECMAScript

Supported

See how this pattern looks (and behaves) in JavaScript's built-in RegExp.

Python (re)

Supported

See how this pattern looks (and behaves) in Python's stdlib `re` module.

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