Merged with chkgrp and renamed to chkusr.

chkgrp-ng.c

@@ -0,0 +1,153 @@
+/**
+ * chkgrp-ng 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
+
+void print_help(const char *prog)
+{
+    printf("Usage: %s [OPTIONS] <username> <groupname>\n", prog);
+    printf("Options:\n");
+    printf("  --passwd PATH    Use custom /etc/passwd file\n");
+    printf("  --group PATH     Use custom /etc/group file\n");
+    printf("  -q               Quiet mode (no output)\n");
+    printf("  -h               Show this help message\n");
+}
+
+const char *get_arg(int *i, int argc, char *argv[], const char *opt)
+{
+    if (*i + 1 >= argc) {
+        fprintf(stderr, "Missing argument after %s\n", opt);
+        exit(2);
+    }
+    return argv[++(*i)];
+}
+
+int get_user_gid(const char *user, const char *passwd_path)
+{
+    FILE *fp = fopen(passwd_path, "r");
+    if (!fp) {
+        fprintf(stderr, "Error: Cannot open passwd file: %s\n", passwd_path);
+        return -1;
+    }
+
+    char line[MAX_LINE];
+    while (fgets(line, sizeof(line), fp)) {
+        char *name = strtok(line, ":");
+        if (!name || strcmp(name, user) != 0) continue;
+
+        strtok(NULL, ":"); // password
+        strtok(NULL, ":"); // UID
+        char *gid_str = strtok(NULL, ":");
+        fclose(fp);
+        return gid_str ? atoi(gid_str) : -1;
+    }
+
+    fclose(fp);
+    return -1;
+}
+
+int check_group(const char *user, const char *group, int user_gid,
+                const char *group_path)
+{
+    FILE *fp = fopen(group_path, "r");
+    if (!fp) {
+        fprintf(stderr, "Error: Cannot open group file: %s\n", group_path);
+        return -1;
+    }
+
+    char line[MAX_LINE];
+    while (fgets(line, sizeof(line), fp)) {
+        char *grp = strtok(line, ":");
+        if (!grp || strcmp(grp, group) != 0) continue;
+
+        strtok(NULL, ":"); // password
+        char *gid_str = strtok(NULL, ":");
+        if (!gid_str) break;
+
+        int group_gid = atoi(gid_str);
+        if (group_gid == user_gid) {
+            fclose(fp);
+            return 1;
+        }
+
+        char *members = strtok(NULL, ":\n");
+        if (!members) break;
+
+        char *m = strtok(members, ",");
+        while (m) {
+            if (strcmp(m, user) == 0) {
+                fclose(fp);
+                return 1;
+            }
+            m = strtok(NULL, ",");
+        }
+
+        fclose(fp);
+        return 0;
+    }
+
+    fclose(fp);
+    return -1;
+}
+
+int main(int argc, char *argv[])
+{
+    const char *passwd_file = "/etc/passwd";
+    const char *group_file  = "/etc/group";
+    int quiet = 0;
+
+    int i = 1;
+    const char *username = NULL, *groupname = NULL;
+
+    while (i < argc) {
+        if (!strcmp(argv[i], "--passwd")) {
+            passwd_file = get_arg(&i, argc, argv, "--passwd");
+        } else if (!strcmp(argv[i], "--group")) {
+            group_file = get_arg(&i, argc, argv, "--group");
+        } else if (!strcmp(argv[i], "-q")) {
+            quiet = 1;
+        } else if (!strcmp(argv[i], "-h")) {
+            print_help(argv[0]);
+            return 0;
+        } else if (!username) {
+            username = argv[i];
+        } else if (!groupname) {
+            groupname = argv[i];
+        } else {
+            fprintf(stderr, "Unexpected argument: %s\n", argv[i]);
+            return 2;
+        }
+        i++;
+    }
+
+    if (!username || !groupname ||
+        strlen(username) > MAX_NAME || strlen(groupname) > MAX_NAME) {
+        return 2;
+    }
+
+    int user_gid = get_user_gid(username, passwd_file);
+    if (user_gid < 0)
+        return 2;
+
+    int result = check_group(username, groupname, user_gid, group_file);
+    if (result == 1) {
+        if (!quiet) puts("Yes");
+        return 0;
+    } else if (result == 0) {
+        if (!quiet) puts("No");
+        return 1;
+    }
+
+    return 2;
+}
+