Merged with chkgrp and renamed to chkusr.

chkgrp-native.c

@@ -0,0 +1,78 @@
+/**
+ * chkgrp-native is a program that checks if a user is a member of a group.
+ *
+ * Author: Johannes Findeisen <you@hanez.org> - 2025
+ * Homepage: https://git.xw3.org/hanez/chkgrp
+ * License: Apache-2.0 (see LICENSE)
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define MAX_LINE 1024
+#define MAX_NAME 256
+
+int main(int argc, char *argv[])
+{
+    if (argc != 3) {
+        fprintf(stderr, "Usage: %s <username> <groupname>\n", argv[0]);
+        return 2;
+    }
+
+    const char *username = argv[1];
+    const char *groupname = argv[2];
+
+    if (strlen(username) > MAX_NAME || strlen(groupname) > MAX_NAME) {
+        fprintf(stderr, "Error: Name too long (max %d characters).\n", MAX_NAME);
+        return 2;
+    }
+
+    FILE *fp = fopen("/etc/group", "r");
+    if (!fp) {
+        perror("Error opening /etc/group");
+        return 2;
+    }
+
+    char line[MAX_LINE];
+    int found = 0;
+
+    while (fgets(line, sizeof(line), fp)) {
+        char *grp_name = strtok(line, ":");
+        if (!grp_name) continue;
+
+        strtok(NULL, ":"); // skip password
+        strtok(NULL, ":"); // skip GID
+
+        char *members = strtok(NULL, ":\n");
+        if (!members) continue;
+
+        if (strcmp(grp_name, groupname) != 0)
+            continue;
+
+        // Group found, now check for user in member list
+        found = 1;
+        char *member = strtok(members, ",");
+        while (member) {
+            if (strcmp(member, username) == 0) {
+                fclose(fp);
+                puts("Yes");
+                return 0;
+            }
+            member = strtok(NULL, ",");
+        }
+
+        break; // no need to continue scanning
+    }
+
+    fclose(fp);
+
+    if (!found) {
+        fprintf(stderr, "Group '%s' not found.\n", groupname);
+        return 2;
+    }
+
+    puts("No");
+    return 1;
+}
+