Text Processingflags: g

Named Capture Group (Date)

Demonstrate named capture groups by extracting year/month/day from ISO-style dates.

Available in

JavaScript / ECMAScript code

jsJavaScript

const re = new RegExp("(?<year>\\d{4})-(?<month>\\d{2})-(?<day>\\d{2})", "g");
const input = "Born 1990-05-21, hired 2018-09-10";
const matches = [...input.matchAll(re)];
console.log(matches.map(m => m[0]));

Uses `String.prototype.matchAll` for global iteration (Node 12+ / all modern browsers).

Python (re) code

pyPython

import re

pattern = re.compile(r"(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})")
input_text = "Born 1990-05-21, hired 2018-09-10"
for m in pattern.finditer(input_text):
    print(m.group(0))

Stdlib `re` module — no third-party dependency. Works on Python 3.6+.

Go (RE2) code

goGo

package main

import (
	"fmt"
	"regexp"
)

func main() {
	re := regexp.MustCompile(`(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})`)
	input := `Born 1990-05-21, hired 2018-09-10`
	for _, match := range re.FindAllString(input, -1) {
		fmt.Println(match)
	}
}

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

Pattern

regexengine-agnostic

(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})   (flags: g)

Raw source: (?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})

How it works

(?<year>\d{4}) captures four digits under the name 'year'; (?<month>\d{2}) and (?<day>\d{2}) likewise. Modern JS, Python 3.7+ (with Python's own `(?P<...>)` spelling — its stdlib `re` has never accepted the JS-style `(?<...>)` form), and Go (which accepts both `(?P<...>)` and, since Go 1.22, `(?<...>)`) all support named capture; the matched substring is accessible by name in code (e.g. m.groups.year in JS, m['year'] in Python).