Initial commit 2.0

.gitignore

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+chkgrp
+chkgrp-min
+chkgrp-native
+chkgrp-native-min
+

LICENSE

@@ -1,4 +1,4 @@
-Copyright 2024 Johannes Findeisen
+Copyright 2025 Johannes Findeisen
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.

Makefile

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+all:
+	$(CC) -Wall -o ./chkgrp ./chkgrp.c
+	$(CC) -Wall -o ./chkgrp-min ./chkgrp-min.c
+	$(CC) -Wall -o ./chkgrp-native ./chkgrp-native.c
+	$(CC) -Wall -o ./chkgrp-native-min ./chkgrp-native-min.c
+
+clean:
+	rm -f ./chkgrp
+	rm -f ./chkgrp-min
+	rm -f ./chkgrp-native
+	rm -f ./chkgrp-native-min
+
+install:
+	install -g 0 -o 0 -m 0655 ./chkgrp /usr/bin/
+	install -g 0 -o 0 -m 0655 ./chkgrp-min /usr/bin/
+	install -g 0 -o 0 -m 0655 ./chkgrp-native /usr/bin/
+	install -g 0 -o 0 -m 0655 ./chkgrp-native-min /usr/bin/
+
+uninstall:
+	rm -f /usr/bin/chkgrp
+	rm -f /usr/bin/chkgrp-min
+	rm -f /usr/bin/chkgrp-native
+	rm -f /usr/bin/chkgrp-native-min
+

README.md

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+# chkgrp
+
+chkgrp is a set of programs to verify if a user is a member of a group on a UNIX based system. This code is so simple that it describes itself very good.
+
+Mor information will follow...
+

chkgrp-min.c

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+/**
+ * chkgrp-min 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>
+#include <pwd.h>
+#include <grp.h>
+
+#define MAX_NAME 256
+
+int main(int argc, char *argv[])
+{
+    if (argc != 3)
+        return 2;
+
+    if (strlen(argv[1]) > MAX_NAME || strlen(argv[2]) > MAX_NAME)
+        return 2;
+
+    struct passwd *pw = getpwnam(argv[1]);
+    if (!pw)
+        return 2;
+
+    struct group *gr = getgrnam(argv[2]);
+    if (!gr)
+        return 2;
+
+    if (pw->pw_gid == gr->gr_gid) {
+        puts("Yes");
+        return 0;
+    }
+
+    for (char **m = gr->gr_mem; *m; ++m) {
+        if (!strcmp(*m, argv[1])) {
+            puts("Yes");
+            return 0;
+        }
+    }
+
+    puts("No");
+    return 1;
+}
+

chkgrp-native-min.c

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+/**
+ * chkgrp-min-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)
+        return 2;
+
+    const char *username = argv[1];
+    const char *groupname = argv[2];
+
+    if (strlen(username) > MAX_NAME || strlen(groupname) > MAX_NAME)
+        return 2;
+
+    FILE *fp = fopen("/etc/group", "r");
+    if (!fp)
+        return 2;
+
+    char line[MAX_LINE];
+    while (fgets(line, sizeof(line), fp)) {
+        char *grp = strtok(line, ":");
+        if (!grp || strcmp(grp, groupname) != 0)
+            continue;
+
+        strtok(NULL, ":"); // skip password
+        strtok(NULL, ":"); // skip GID
+
+        char *members = strtok(NULL, ":\n");
+        if (!members) break;
+
+        char *m = strtok(members, ",");
+        while (m) {
+            if (!strcmp(m, username)) {
+                puts("Yes");
+                fclose(fp);
+                return 0;
+            }
+            m = strtok(NULL, ",");
+        }
+
+        break; // group matched, no user found
+    }
+
+    fclose(fp);
+    puts("No");
+    return 1;
+}
+

chkgrp-native.c

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+/**
+ * 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;
+}
+

chkgrp.c

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+/**
+ * chkgrp 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>
+#include <pwd.h>
+#include <grp.h>
+#include <unistd.h>
+#include <errno.h>
+#include <limits.h>
+
+#ifndef LOGIN_NAME_MAX
+#define LOGIN_NAME_MAX 256
+#endif
+
+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];
+
+    // Runtime check for max name length
+    long max_name_len = sysconf(_SC_LOGIN_NAME_MAX);
+    if (max_name_len <= 0 || max_name_len > 1024) {
+        max_name_len = LOGIN_NAME_MAX;
+    }
+
+    if (strlen(username) > (size_t)max_name_len) {
+        fprintf(stderr, "Error: Username too long (max %ld characters).\n",
+                max_name_len);
+        return 2;
+    }
+
+    if (strlen(groupname) > (size_t)max_name_len) {
+        fprintf(stderr, "Error: Group name too long (max %ld characters).\n",
+                max_name_len);
+        return 2;
+    }
+
+    struct passwd *pw = getpwnam(username);
+    if (!pw) {
+        fprintf(stderr, "Error: User '%s' not found.\n", username);
+        return 2;
+    }
+
+    struct group *gr = getgrnam(groupname);
+    if (!gr) {
+        fprintf(stderr, "Error: Group '%s' not found.\n", groupname);
+        return 2;
+    }
+
+    if (pw->pw_gid == gr->gr_gid) {
+        puts("Yes");
+        return 0;
+    }
+
+    for (char **members = gr->gr_mem; *members != NULL; members++) {
+        if (strcmp(*members, username) == 0) {
+            puts("Yes");
+            return 0;
+        }
+    }
+
+    puts("No");
+    return 1;
+}
+