getopt

ansicodes/Makefile

@@ -0,0 +1,14 @@
+CC = gcc
+CFLAGS = -Wall -O2
+
+TARGET = main.elf
+SRC = main.c
+
+#LDFLAGS =
+
+$(TARGET): $(SRC)
+	@echo CC $@
+	@$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+
+clean:
+	rm -f $(TARGET)

ansicodes/ansi.h

@@ -0,0 +1,64 @@
+#ifndef ANSI_H
+#define ANSI_H
+
+/* Set this to make all the codes no-ops */
+//#define ANSI_DISABLE
+
+#ifndef ANSI_DISABLE
+#define ESC(x) x
+#else
+#define ESC(x)
+#endif
+
+/* Reset */
+#define ANSI_RESET ESC("\033[0m")
+
+/* Styles */
+#define ANSI_BOLD   ESC("\033[1m")
+#define ANSI_DIM    ESC("\033[2m")
+#define ANSI_UNDER  ESC("\033[4m")
+#define ANSI_BLINK  ESC("\033[5m")
+#define ANSI_REV    ESC("\033[7m")
+#define ANSI_HIDDEN ESC("\033[8m")
+
+/* Foreground colors */
+#define ANSI_FG_BLACK   ESC("\033[30m")
+#define ANSI_FG_RED     ESC("\033[31m")
+#define ANSI_FG_GREEN   ESC("\033[32m")
+#define ANSI_FG_YELLOW  ESC("\033[33m")
+#define ANSI_FG_BLUE    ESC("\033[34m")
+#define ANSI_FG_MAGENTA ESC("\033[35m")
+#define ANSI_FG_CYAN    ESC("\033[36m")
+#define ANSI_FG_WHITE   ESC("\033[37m")
+
+/* Bright foreground colors */
+#define ANSI_FG_BBLACK   ESC("\033[90m")
+#define ANSI_FG_BRED     ESC("\033[91m")
+#define ANSI_FG_BGREEN   ESC("\033[92m")
+#define ANSI_FG_BYELLOW  ESC("\033[93m")
+#define ANSI_FG_BBLUE    ESC("\033[94m")
+#define ANSI_FG_BMAGENTA ESC("\033[95m")
+#define ANSI_FG_BCYAN    ESC("\033[96m")
+#define ANSI_FG_BWHITE   ESC("\033[97m")
+
+/* Background colors */
+#define ANSI_BG_BLACK   ESC("\033[40m")
+#define ANSI_BG_RED     ESC("\033[41m")
+#define ANSI_BG_GREEN   ESC("\033[42m")
+#define ANSI_BG_YELLOW  ESC("\033[43m")
+#define ANSI_BG_BLUE    ESC("\033[44m")
+#define ANSI_BG_MAGENTA ESC("\033[45m")
+#define ANSI_BG_CYAN    ESC("\033[46m")
+#define ANSI_BG_WHITE   ESC("\033[47m")
+
+/* Bright background colors */
+#define ANSI_BG_BBLACK   ESC("\033[100m")
+#define ANSI_BG_BRED     ESC("\033[101m")
+#define ANSI_BG_BGREEN   ESC("\033[102m")
+#define ANSI_BG_BYELLOW  ESC("\033[103m")
+#define ANSI_BG_BBLUE    ESC("\033[104m")
+#define ANSI_BG_BMAGENTA ESC("\033[105m")
+#define ANSI_BG_BCYAN    ESC("\033[106m")
+#define ANSI_BG_BWHITE   ESC("\033[107m")
+
+#endif // ANSI_H

ansicodes/main.c

@@ -0,0 +1,58 @@
+#include "ansi.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+int main(int argc, char *argv[]) {
+
+    if (!isatty(STDOUT_FILENO) || !(getenv("TERM") && strcmp(getenv("TERM"), "dumb") != 0)) {
+        printf("This terminal does not seem to support ANSI\n");
+        exit(EXIT_FAILURE);
+    }
+
+    printf(ANSI_BOLD "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_DIM "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_UNDER "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_BLINK "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_REV "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_HIDDEN "ABCDE" ANSI_RESET "\n");
+
+    printf(ANSI_FG_BLACK "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_FG_RED "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_FG_GREEN "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_FG_YELLOW "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_FG_BLUE "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_FG_MAGENTA "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_FG_CYAN "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_FG_WHITE "ABCDE" ANSI_RESET "\n");
+
+    printf(ANSI_FG_BBLACK "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_FG_BRED "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_FG_BGREEN "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_FG_BYELLOW "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_FG_BBLUE "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_FG_BMAGENTA "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_FG_BCYAN "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_FG_BWHITE "ABCDE" ANSI_RESET "\n");
+
+    printf(ANSI_BG_BLACK "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_BG_RED "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_BG_GREEN "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_BG_YELLOW "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_BG_BLUE "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_BG_MAGENTA "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_BG_CYAN "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_BG_WHITE "ABCDE" ANSI_RESET "\n");
+
+    printf(ANSI_BG_BBLACK "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_BG_BRED "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_BG_BGREEN "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_BG_BYELLOW "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_BG_BBLUE "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_BG_BMAGENTA "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_BG_BCYAN "ABCDE" ANSI_RESET "\n");
+    printf(ANSI_BG_BWHITE "ABCDE" ANSI_RESET "\n");
+
+    exit(EXIT_SUCCESS);
+}

config_ini/conf.c

@@ -57,6 +57,13 @@ Config *config_load(const char *filename) {
     return cfg;
 }
 
+ConfigEntry *config_get_next(ConfigEntry *entry, int *index) {
+    if (!entry)
+        return NULL;
+
+    return (0 == (*index)++) ? entry : entry->next;
+}
+
 /* Get value for a key */
 const char *config_get(Config *cfg, const char *key) {
     for (ConfigEntry *e = cfg->head; e; e = e->next) {

config_ini/conf.h

@@ -11,8 +11,9 @@ typedef struct {
     ConfigEntry *head;
 } Config;
 
-Config     *config_load(const char *filename);
-const char *config_get(Config *cfg, const char *key);
-void        config_free(Config *cfg);
+Config      *config_load(const char *filename);
+const char  *config_get(Config *cfg, const char *key);
+ConfigEntry *config_get_next(ConfigEntry *entry, int *index);
+void         config_free(Config *cfg);
 
 #endif // CONF_H

config_ini/main.c

@@ -1,8 +1,53 @@
 #include "conf.h"
+#include <fcntl.h>
 #include <stdio.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <unistd.h>
 
-// Example usage
 int main(void) {
+    const char *home = getenv("HOME");
+    if (!home) {
+        perror("home");
+        exit(EXIT_FAILURE);
+    }
+
+    /* Potentially scope this to preserve stack if thats an issue */
+    char config_dir[256];
+    char config_file[512];
+
+    {
+        snprintf(config_dir, sizeof(config_dir), "%s/.config", home);
+        snprintf(config_file, sizeof(config_file), "%s/mytool.ini", config_dir);
+
+        /* Ensure ~/.config exists */
+        struct stat st;
+        if (stat(config_dir, &st) == 0) {
+            if (!S_ISDIR(st.st_mode)) {
+                printf("Creating config directory\n");
+                mkdir(config_dir, 0700);
+                perror("mkdir ~/.config");
+            }
+        }
+
+        /* Create config file */
+        int fd = open(config_file, O_RDWR | O_CREAT, 0600);
+        if (fd < 0) {
+            perror("open mytool.ini");
+            return 1;
+        }
+        close(fd);
+    }
+
+    FILE *f = fopen(config_file, "r");
+    if (!f) {
+        perror("fopen");
+        return 1;
+    }
+    /* Parsing here ... */
+    fclose(f);
+    unlink(config_file);
+
     Config *cfg = config_load("config.ini");
     if (!cfg) {
         fprintf(stderr, "Failed to load config.ini\n");
@@ -15,6 +60,15 @@ int main(void) {
     printf("Username: %s\n", user ? user : "(not set)");
     printf("Password: %s\n", pass ? pass : "(not set)");
 
+    printf("-----\n");
+
+    /* Iterate over config values */
+    ConfigEntry *c = cfg->head;
+    int          idx = 0;
+    while ((c = config_get_next(c, &idx)) != NULL) {
+        printf("%s = %s\n", c->key, c->value);
+    }
+
     config_free(cfg);
     return 0;
 }

crc32/Makefile

@@ -0,0 +1,12 @@
+CC ?= gcc
+CFLAGS ?= -Wall -O2
+
+TARGET = test.elf
+SRC = test.c
+
+$(TARGET): $(SRC)
+	@echo CC $@
+	@$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+
+clean:
+	rm -f $(TARGET)

crc32/crc32.h

@@ -0,0 +1,78 @@
+#ifndef CRC32_H
+#define CRC32_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+/*
+ * CRC-32 (IEEE 802.3, gzip, zip, etc.)
+ * Polynomial: 0xEDB88320 (reflected)
+ * Init value: 0xFFFFFFFF
+ * Final XOR: 0xFFFFFFFF
+ */
+
+#define CRC32_INIT ((uint32_t)0xFFFFFFFFU)
+#define CRC32_XOR  ((uint32_t)0xFFFFFFFFU)
+
+static const uint32_t crc32_table[256] = {
+    0x00000000U, 0x77073096U, 0xEE0E612CU, 0x990951BAU, 0x076DC419U, 0x706AF48FU, 0xE963A535U, 0x9E6495A3U, 0x0EDB8832U,
+    0x79DCB8A4U, 0xE0D5E91EU, 0x97D2D988U, 0x09B64C2BU, 0x7EB17CBDU, 0xE7B82D07U, 0x90BF1D91U, 0x1DB71064U, 0x6AB020F2U,
+    0xF3B97148U, 0x84BE41DEU, 0x1ADAD47DU, 0x6DDDE4EBU, 0xF4D4B551U, 0x83D385C7U, 0x136C9856U, 0x646BA8C0U, 0xFD62F97AU,
+    0x8A65C9ECU, 0x14015C4FU, 0x63066CD9U, 0xFA0F3D63U, 0x8D080DF5U, 0x3B6E20C8U, 0x4C69105EU, 0xD56041E4U, 0xA2677172U,
+    0x3C03E4D1U, 0x4B04D447U, 0xD20D85FDU, 0xA50AB56BU, 0x35B5A8FAU, 0x42B2986CU, 0xDBBBC9D6U, 0xACBCF940U, 0x32D86CE3U,
+    0x45DF5C75U, 0xDCD60DCFU, 0xABD13D59U, 0x26D930ACU, 0x51DE003AU, 0xC8D75180U, 0xBFD06116U, 0x21B4F4B5U, 0x56B3C423U,
+    0xCFBA9599U, 0xB8BDA50FU, 0x2802B89EU, 0x5F058808U, 0xC60CD9B2U, 0xB10BE924U, 0x2F6F7C87U, 0x58684C11U, 0xC1611DABU,
+    0xB6662D3DU, 0x76DC4190U, 0x01DB7106U, 0x98D220BCU, 0xEFD5102AU, 0x71B18589U, 0x06B6B51FU, 0x9FBFE4A5U, 0xE8B8D433U,
+    0x7807C9A2U, 0x0F00F934U, 0x9609A88EU, 0xE10E9818U, 0x7F6A0DBBU, 0x086D3D2DU, 0x91646C97U, 0xE6635C01U, 0x6B6B51F4U,
+    0x1C6C6162U, 0x856530D8U, 0xF262004EU, 0x6C0695EDU, 0x1B01A57BU, 0x8208F4C1U, 0xF50FC457U, 0x65B0D9C6U, 0x12B7E950U,
+    0x8BBEB8EAU, 0xFCB9887CU, 0x62DD1DDFU, 0x15DA2D49U, 0x8CD37CF3U, 0xFBD44C65U, 0x4DB26158U, 0x3AB551CEU, 0xA3BC0074U,
+    0xD4BB30E2U, 0x4ADFA541U, 0x3DD895D7U, 0xA4D1C46DU, 0xD3D6F4FBU, 0x4369E96AU, 0x346ED9FCU, 0xAD678846U, 0xDA60B8D0U,
+    0x44042D73U, 0x33031DE5U, 0xAA0A4C5FU, 0xDD0D7CC9U, 0x5005713CU, 0x270241AAU, 0xBE0B1010U, 0xC90C2086U, 0x5768B525U,
+    0x206F85B3U, 0xB966D409U, 0xCE61E49FU, 0x5EDEF90EU, 0x29D9C998U, 0xB0D09822U, 0xC7D7A8B4U, 0x59B33D17U, 0x2EB40D81U,
+    0xB7BD5C3BU, 0xC0BA6CADU, 0xEDB88320U, 0x9ABFB3B6U, 0x03B6E20CU, 0x74B1D29AU, 0xEAD54739U, 0x9DD277AFU, 0x04DB2615U,
+    0x73DC1683U, 0xE3630B12U, 0x94643B84U, 0x0D6D6A3EU, 0x7A6A5AA8U, 0xE40ECF0BU, 0x9309FF9DU, 0x0A00AE27U, 0x7D079EB1U,
+    0xF00F9344U, 0x8708A3D2U, 0x1E01F268U, 0x6906C2FEU, 0xF762575DU, 0x806567CBU, 0x196C3671U, 0x6E6B06E7U, 0xFED41B76U,
+    0x89D32BE0U, 0x10DA7A5AU, 0x67DD4ACCU, 0xF9B9DF6FU, 0x8EBEEFF9U, 0x17B7BE43U, 0x60B08ED5U, 0xD6D6A3E8U, 0xA1D1937EU,
+    0x38D8C2C4U, 0x4FDFF252U, 0xD1BB67F1U, 0xA6BC5767U, 0x3FB506DDU, 0x48B2364BU, 0xD80D2BDAU, 0xAF0A1B4CU, 0x36034AF6U,
+    0x41047A60U, 0xDF60EFC3U, 0xA867DF55U, 0x316E8EEFU, 0x4669BE79U, 0xCB61B38CU, 0xBC66831AU, 0x256FD2A0U, 0x5268E236U,
+    0xCC0C7795U, 0xBB0B4703U, 0x220216B9U, 0x5505262FU, 0xC5BA3BBEU, 0xB2BD0B28U, 0x2BB45A92U, 0x5CB36A04U, 0xC2D7FFA7U,
+    0xB5D0CF31U, 0x2CD99E8BU, 0x5BDEAE1DU, 0x9B64C2B0U, 0xEC63F226U, 0x756AA39CU, 0x026D930AU, 0x9C0906A9U, 0xEB0E363FU,
+    0x72076785U, 0x05005713U, 0x95BF4A82U, 0xE2B87A14U, 0x7BB12BAEU, 0x0CB61B38U, 0x92D28E9BU, 0xE5D5BE0DU, 0x7CDCEFB7U,
+    0x0BDBDF21U, 0x86D3D2D4U, 0xF1D4E242U, 0x68DDB3F8U, 0x1FDA836EU, 0x81BE16CDU, 0xF6B9265BU, 0x6FB077E1U, 0x18B74777U,
+    0x88085AE6U, 0xFF0F6A70U, 0x66063BCAU, 0x11010B5CU, 0x8F659EFFU, 0xF862AE69U, 0x616BFFD3U, 0x166CCF45U, 0xA00AE278U,
+    0xD70DD2EEU, 0x4E048354U, 0x3903B3C2U, 0xA7672661U, 0xD06016F7U, 0x4969474DU, 0x3E6E77DBU, 0xAED16A4AU, 0xD9D65ADCU,
+    0x40DF0B66U, 0x37D83BF0U, 0xA9BCAE53U, 0xDEBB9EC5U, 0x47B2CF7FU, 0x30B5FFE9U, 0xBDBDF21CU, 0xCABAC28AU, 0x53B39330U,
+    0x24B4A3A6U, 0xBAD03605U, 0xCDD70693U, 0x54DE5729U, 0x23D967BFU, 0xB3667A2EU, 0xC4614AB8U, 0x5D681B02U, 0x2A6F2B94U,
+    0xB40BBE37U, 0xC30C8EA1U, 0x5A05DF1BU, 0x2D02EF8DU,
+};
+
+static inline uint32_t crc32_update_raw(uint32_t crc, const void *data, unsigned int length) {
+    const uint8_t *p = (const uint8_t *)data;
+    while (length--) {
+        crc = (crc >> 8) ^ crc32_table[(crc ^ *p++) & 0xFFU];
+    }
+    return crc;
+}
+
+static inline uint32_t crc32(const void *data, unsigned int length) {
+    uint32_t crc = CRC32_INIT;
+    crc = crc32_update_raw(crc, data, length);
+    return crc ^ CRC32_XOR;
+}
+
+static inline uint32_t crc32_init(void) {
+    return CRC32_INIT;
+}
+
+static inline uint32_t crc32_update(uint32_t crc, const void *data, unsigned int length) {
+    return crc32_update_raw(crc, data, length);
+}
+
+static inline uint32_t crc32_finalize(uint32_t crc) {
+    return crc ^ CRC32_XOR;
+}
+
+#undef CRC32_XOR
+#undef CRC32_INIT
+
+#endif // CRC32_H

crc32/crc32_nolookup.h

@@ -0,0 +1,33 @@
+#ifndef CRC32_NOLOOKUP_H
+#define CRC32_NOLOOKUP_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+/*
+ * CRC-32 (IEEE 802.3) implementation
+ * Polynomial: 0xEDB88320 (reflected)
+ * Initial value: 0xFFFFFFFF
+ * Final XOR: 0xFFFFFFFF
+ * Input reflected: Yes
+ * Output reflected: Yes
+ */
+
+static inline uint32_t crc32_ieee(const void *data, size_t len) {
+    const uint8_t *p = (const uint8_t *)data;
+    uint32_t       crc = 0xFFFFFFFF;
+
+    while (len--) {
+        crc ^= *p++;
+        for (int i = 0; i < 8; i++) {
+            if (crc & 1)
+                crc = (crc >> 1) ^ 0xEDB88320;
+            else
+                crc >>= 1;
+        }
+    }
+
+    return crc ^ 0xFFFFFFFF;
+}
+
+#endif // CRC32_H

crc32/test.c

@@ -0,0 +1,33 @@
+#include "crc32.h"
+#include "crc32_nolookup.h"
+#include <assert.h>
+#include <stdio.h>
+
+int main(void) {
+    assert(crc32("123456789", 9) == 0xCBF43926);
+    assert(crc32("", 0) == 0x00000000);
+    assert(crc32("a", 1) == 0xE8B7BE43);
+    assert(crc32("A", 1) == 0xD3D99E8B);
+    assert(crc32("hello", 5) == 0x3610A686);
+    assert(crc32("The quick brown fox jumps over the lazy dog", 43) == 0x414FA339);
+    assert(crc32("The quick brown fox jumps over the lazy dog.", 44) == 0x519025E9);
+
+    /* Keep in mind the update api requires initialization and finalization */
+    uint32_t crc = crc32_init();
+    crc = crc32_update_raw(crc, "a", 1);
+    crc = crc32_finalize(crc);
+
+    assert(crc == crc32("a", 1));
+    assert(crc == 0xE8B7BE43);
+
+    assert(crc32_ieee("123456789", 9) == 0xCBF43926);
+    assert(crc32_ieee("", 0) == 0x00000000);
+    assert(crc32_ieee("a", 1) == 0xE8B7BE43);
+    assert(crc32_ieee("A", 1) == 0xD3D99E8B);
+    assert(crc32_ieee("hello", 5) == 0x3610A686);
+    assert(crc32_ieee("The quick brown fox jumps over the lazy dog", 43) == 0x414FA339);
+    assert(crc32_ieee("The quick brown fox jumps over the lazy dog.", 44) == 0x519025E9);
+
+    printf("All good!\n");
+    return 0;
+}

freelist/hexdump.c

@@ -2,30 +2,31 @@
 #include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
 
-void hexdump(const void *data, size_t size) {
+void hexdump(const void *data, const size_t size, const size_t width) {
     const unsigned char *p = (const unsigned char *)data;
     size_t               i, j;
 
-    for (i = 0; i < size; i += 16) {
-        // Print offset
+    for (i = 0; i < size; i += width) {
         printf("%08zx  ", i);
 
-        // Print hex bytes
-        for (j = 0; j < 16; j++) {
+        for (j = 0; j < width; j++) {
             if (i + j < size) {
                 printf("%02X ", p[i + j]);
             } else {
-                printf("   "); // padding for incomplete lines
+                printf("   ");
             }
-            if (j == 7)
-                printf(" "); // extra space in middle
+
+            if ((j + 1) % 8 == 0)
+                printf(" ");
         }
 
         printf(" |");
 
-        // Print ASCII characters
-        for (j = 0; j < 16 && i + j < size; j++) {
+        for (j = 0; j < width && i + j < size; j++) {
             unsigned char c = p[i + j];
             printf("%c", isprint(c) ? c : '.');
         }

freelist/hexdump.h

@@ -3,6 +3,6 @@
 
 #include <stddef.h>
 
-void hexdump(const void *data, size_t size);
+void hexdump(const void *data, const size_t size, const size_t width);
 
 #endif // HEXDUMP_H

freelist/main.c

@@ -47,7 +47,7 @@ int main() {
     const uint32_t head_crc = crc32(headblock, BUFFER_SIZE / 2);
 
     /* Display a nice hexdump so you can see the layout */
-    hexdump(headblock, BUFFER_SIZE * 2);
+    hexdump(headblock, BUFFER_SIZE * 2, 32);
 
     if (!fl_init(&fl, (uintptr_t)mem, BUFFER_SIZE, sizeof(Vec3))) {
         printf("Freelist failed to initialize!\n");
@@ -130,7 +130,7 @@ int main() {
     assert(crc32(tailblock, BUFFER_SIZE / 2) == tail_crc);
 
     /* Hexdump the heap, free the block and declare victory */
-    hexdump(headblock, BUFFER_SIZE * 2);
+    hexdump(headblock, BUFFER_SIZE * 2, 32);
     free(headblock);
     printf("All tests passed!\n");
     return 0;

getopt/Makefile

@@ -0,0 +1,15 @@
+CC = gcc
+CFLAGS = -Wall -O2
+
+all: getopt.elf getopt_long.elf
+
+getopt.elf: getopt.c
+	@echo CC $@
+	@$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+
+getopt_long.elf: getopt_long.c
+	@echo CC $@
+	@$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+
+clean:
+	rm -f *.elf

getopt/getopt.c

@@ -0,0 +1,15 @@
+#include <stdio.h>
+#include <unistd.h>
+
+int main(int argc, char *argv[]) {
+    int opt;
+    while ((opt = getopt(argc, argv, "hf:o:")) != -1) {
+        switch (opt) {
+        case 'h': puts("Help"); break;
+        case 'f': printf("File: %s\n", optarg); break;
+        case 'o': printf("Output: %s\n", optarg); break;
+        default: fprintf(stderr, "Usage: %s [-h] [-f file] [-o output]\n", argv[0]); return 1;
+        }
+    }
+    return 0;
+}

getopt/getopt_long.c

@@ -0,0 +1,38 @@
+#include <getopt.h>
+#include <stdio.h>
+#include <string.h>
+
+#define VERSION "0.0.1"
+
+int main(int argc, char *argv[]) {
+    int                  opt;
+    int                  option_index = 0;
+    static struct option long_opts[] = {
+        {"help", no_argument, 0, 'h'},
+        {"file", required_argument, 0, 'f'},
+        {"output", required_argument, 0, 'o'},
+        {"version", no_argument, 0, 'v'},
+        {0, 0, 0, 0},
+    };
+
+    int  has_file = 0;
+    char a[128];
+
+    while ((opt = getopt_long(argc, argv, "hvf:o:", long_opts, &option_index)) != -1) {
+        switch (opt) {
+        case 'h': puts("Help"); break;
+        case 'f':
+            printf("File: %s\n", optarg);
+            strncpy(a, optarg, 127);
+            has_file = 1;
+            break;
+        case 'o': printf("Output: %s\n", optarg); break;
+        case 'v': printf("Version: v%s\n", VERSION); break;
+        default: return 1;
+        }
+    }
+
+    if (has_file)
+        printf("Using file: %s\n", a);
+    return 0;
+}

mmap_file/.gitignore

@@ -0,0 +1 @@
+mapped.txt

mmap_file/Makefile

@@ -0,0 +1,12 @@
+CC ?= gcc
+CFLAGS ?= -Wall -O2
+
+TARGET = main.elf
+SRC = mmap_file.c
+
+$(TARGET): $(SRC)
+	@echo CC $@
+	@$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+
+clean:
+	rm -f $(TARGET)

mmap_file/mmap_file.c

@@ -0,0 +1,56 @@
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#define FILE_PATH "mapped.txt"
+#define FILE_SIZE 4096
+
+int main() {
+    int fd = open(FILE_PATH, O_RDWR | O_CREAT, 0644);
+    if (fd == -1) {
+        perror("open");
+        return 1;
+    }
+
+    /* We want some space to write */
+    if (ftruncate(fd, FILE_SIZE) == -1) {
+        perror("ftruncate");
+        close(fd);
+        return 1;
+    }
+
+    /* NULL means we do not care where the mapping goes, anywhere in canonical memory will do
+     * PROT_READ/WRITE are just protection flags that allows our process rw rights
+     * MAP_SHARED means our (real time, or close to) changes are visible to other processes mmping the same file */
+    void *file_memory = mmap(NULL, FILE_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+    if (file_memory == MAP_FAILED) {
+        perror("mmap");
+        close(fd);
+        return 1;
+    }
+
+    const char *message = "This is written to file!";
+    strncpy(file_memory, message, strlen(message) + 1);
+
+    /* Re-truncate the file to known length, otherwise the entire buffer
+     * (4k, with garbage from whatever the kernel gave us) will be in the file*/
+    if (ftruncate(fd, strnlen(message, FILE_SIZE + 1)) == -1) {
+        perror("ftruncate");
+        close(fd);
+        return 1;
+    }
+
+    printf("Mapped region content: %s\n", (char *)file_memory);
+
+    munmap(file_memory, FILE_SIZE);
+
+    close(fd);
+
+    /* Optional finishing step, but i assume you want to inspect the file */
+    // remove(file_path);
+
+    return 0;
+}

syslog/Makefile

@@ -0,0 +1,14 @@
+CC = gcc
+CFLAGS = -Wall -Wextra -O2
+
+TARGET = main.elf
+SRC = main.c
+
+#LDFLAGS =
+
+$(TARGET): $(SRC)
+	@echo CC $@
+	@$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+
+clean:
+	rm -f $(TARGET)

syslog/main.c

@@ -0,0 +1,24 @@
+#include <stdlib.h>
+#include <syslog.h>
+
+/*
+ * For unix systems:
+ *      tail /var/log/messages
+ *
+ * For systems using systemd:
+ *      journalctl -t my_daemon
+ */
+
+#define NAME "my_program"
+
+int main(void) {
+    /* LOG_PID ,LOG_CONS ,LOG_ODELAY ,LOG_NDELAY ,LOG_NOWAIT ,LOG_PERROR */
+    openlog(NAME, LOG_PID | LOG_CONS, LOG_USER);
+
+    /* LOG_EMERG, LOG_ALERT, LOG_CRIT, LOG_ERR, LOG_WARNING, LOG_NOTICE, LOG_INFO, LOG_DEBUG */
+    syslog(LOG_INFO, "Hello, log!");
+    syslog(LOG_INFO, "Formatting works %s!", "as well");
+
+    closelog();
+    return EXIT_SUCCESS;
+}

walk.c

@@ -0,0 +1,70 @@
+#include <dirent.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+void walk_dir(const char *path, int follow_symlinks, int ignore_hidden) {
+    DIR *dir = opendir(path);
+    if (!dir) {
+        perror(path);
+        return;
+    }
+
+    struct dirent *entry;
+    while ((entry = readdir(dir)) != NULL) {
+        if (strncmp(entry->d_name, ".", 1) == 0)
+            continue;
+
+        if (strncmp(entry->d_name, "..", 2) == 0)
+            continue;
+
+        // Skip hidden files if requested
+        if (ignore_hidden && entry->d_name[0] == '.')
+            continue;
+
+        char fullpath[4096];
+        snprintf(fullpath, sizeof(fullpath), "%s/%s", path, entry->d_name);
+
+        struct stat st;
+        int         ret;
+        if (follow_symlinks)
+            ret = stat(fullpath, &st);
+        else
+            ret = lstat(fullpath, &st);
+
+        if (ret != 0) {
+            /* Permission denied ends up here */
+            perror(fullpath);
+            continue;
+        }
+
+        /* There are a bunch of macros in <sys/stat.h> like S_ISDIR for checking */
+        printf("FILE: %s\n", fullpath);
+        if (S_ISDIR(st.st_mode)) {
+            walk_dir(fullpath, follow_symlinks, ignore_hidden);
+        } 
+    }
+
+    closedir(dir);
+}
+
+int main(int argc, char *argv[]) {
+    if (argc < 2) {
+        fprintf(stderr, "Usage: %s <dir> [--follow-symlinks] [--ignore-hidden]\n", argv[0]);
+        return 1;
+    }
+
+    int follow_symlinks = 0;
+    int ignore_hidden = 0;
+
+    for (int i = 2; i < argc; i++) {
+        if (strcmp(argv[i], "--follow-symlinks") == 0)
+            follow_symlinks = 1;
+        if (strcmp(argv[i], "--ignore-hidden") == 0)
+            ignore_hidden = 1;
+    }
+
+    walk_dir(argv[1], follow_symlinks, ignore_hidden);
+    return 0;
+}