PEM Certificate Block in GO
Go (RE2) can't run this pattern out of the box.
Try it in the GO tester →Why it doesn't work in GO
Go's RE2 engine doesn't support backreferences (`\1`, `\2`, …) for the same linear-time reason.
Approach
Match the candidate substring with a single capture, then verify the duplication in code; or use JS / Python which both support backreferences.
Workaround code in Go (RE2)
goGo (workaround)
package main
import (
"fmt"
"regexp"
)
// RE2 doesn't support backreferences. The fix: capture the candidate
// substring once, then verify the duplication in Go code.
//
// Example: instead of `(\w+)\s+\1` (duplicate words), capture two
// adjacent words and compare them.
func main() {
re := regexp.MustCompile(`\b(\w+)\s+(\w+)\b`)
input := "the cat cat ran ran fast"
for _, m := range re.FindAllStringSubmatch(input, -1) {
if m[1] == m[2] { // the backreference equality, in code
fmt.Println(m[0])
}
}
}Capture the candidate substrings as separate groups, then compare them in Go code instead of via a backreference.
Pattern
regexGO
-----BEGIN ([A-Z ]+)-----([\s\S]+?)-----END \1----- (flags: g)How the pattern works
-----BEGIN ([A-Z ]+)----- captures the block type label (e.g. CERTIFICATE, RSA PRIVATE KEY). ([\s\S]+?) lazily captures the multiline base64 body. \1 back-references the type to ensure BEGIN and END labels match. The dotAll behaviour requires [\s\S] in JS (or /s flag in newer JS) and re.DOTALL in Python.
Examples
Input
-----BEGIN CERTIFICATE-----\nMIIBkTCB+...\n-----END CERTIFICATE-----Matches
-----BEGIN CERTIFICATE-----\nMIIBkTCB+...\n-----END CERTIFICATE-----
Input
-----BEGIN RSA PRIVATE KEY-----\nMIIEow...\n-----END RSA PRIVATE KEY-----Matches
-----BEGIN RSA PRIVATE KEY-----\nMIIEow...\n-----END RSA PRIVATE KEY-----