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Date: Mon, 10 Jun 2024 05:38:36 +0000
From: Nigel Kukard <>
To: "" <>
Subject: Different results with regex.h between Musl and Libc

Hi there,

I'm wondering if someone could possibly point out what I'm doing wrong here.

I tried searching the mailing list for similar topics, I found some 
relating to POSIX regex but none that really dealt with this issue with 
extended regex. I also didn't find anything really addressing this on

If I missed something I'm terribly sorry.

Musl output (Alpine 3.20), musl-1.2.5-r1...

The input '37' matches the pattern '^([0-9]*)?\.?([0-9]*)?$'
Match 0: 37
Match 1:
Match 2: 37

Glibc output (ArchLinux), glibc 2.39+r52+gf8e4623421-1...

The input '37' matches the pattern '^([0-9]*)?\.?([0-9]*)?$'
Match 0: 37
Match 1: 37
Match 2:

Test code...
#include <stdio.h>
#include <regex.h>

int main() {
     const char *pattern = "^([0-9]*)?\\.?([0-9]*)?$";
     const char *input = "37";
     regex_t regex;
     regmatch_t matches[3];
     int ret;

     ret = regcomp(&regex, pattern, REG_EXTENDED);
     if (ret) {
         fprintf(stderr, "Could not compile regex\n");
         return 1;

     ret = regexec(&regex, input, 3, matches, 0);
     if (!ret) {
         printf("The input '%s' matches the pattern '%s'\n", input, 
         for (int i = 0; i < 3; i++) {
             if (matches[i].rm_so != -1) {
                 printf("Match %d: %.*s\n", i, matches[i].rm_eo - 
matches[i].rm_so, input + matches[i].rm_so);
     } else if (ret == REG_NOMATCH) {
         printf("The input '%s' does not match the pattern '%s'\n", 
input, pattern);
     } else {
         char msgbuf[100];
         regerror(ret, &regex, msgbuf, sizeof(msgbuf));
         fprintf(stderr, "Regex match failed: %s\n", msgbuf);
         return 1;


     return 0;

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