1 files changed, 145 insertions, 0 deletions
diff --git a/src/commands/head.c b/src/commands/head.c
new file mode 100644
index 0000000..446a9e6
--- /dev/null
+++ b/src/commands/head.c
@@ -0,0 +1,145 @@
+#include "../command.h"
+
+#include <stdio.h>
+#include <string.h>
+
+struct Flags {
+    int count;
+    bool lines;
+    bool print_headers;
+    bool dont_print_headers;
+};
+
+static void head_file_lines(FILE* file, struct Flags* flags) {
+    size_t len = 0;
+    char* line = NULL;
+
+    int count = flags->count;
+    while(count > 0 && getline(&line, &len, file) != -1) {
+        printf("%s", line);
+        count--;
+    }
+
+    free(line);
+    fclose(file);
+}
+
+static void head_file_chars(FILE* file, struct Flags* flags) {
+    char c;
+    int count = flags->count;
+    while(count > 0 && (c = getc(file)) != EOF) {
+        putchar(c);
+        count--;
+    }
+
+    fclose(file);
+}
+
+static void help() {
+    printf("Usage: head [OPTIONS] [FILE]...\n\n");
+    printf("Print first 10 lines of FILEs (or stdin)\n");
+    printf("With more than one FILE, precede each with a filename header.\n\n");
+    printf("\t-c [+]N[bkm]\tPrint first N bytes\n");
+	printf("\t-n N[bkm]\tPrint first N lines\n");
+	printf("\t\t\t(b:*512 k:*1024 m:*1024^2)\n");
+	printf("\t-q\t\tNever print headers\n");
+	printf("\t-v\t\tAlways print headers\n");
+    exit(EXIT_SUCCESS);
+}
+
+static char* next_arg(int argc, char** argv, int index) {
+    if (index >= argc) {
+        error("error: expected another argument after option");
+    }
+    return argv[index];
+}
+
+static void print_header(char* path, struct Flags* flags, bool many) {
+    if (flags->dont_print_headers) return;
+    if (!many && !flags->print_headers) return;
+    if (streql("-", path)) {
+        printf("\n==> standard input <==\n");
+    } else {
+        printf("\n=>> %s <==\n", path);
+    }
+}
+
+static void head_file(char* path, struct Flags* flags, bool many) {
+    FILE* file = get_file(path, "r");
+    print_header(path, flags, many);
+    if (flags->lines) {
+        head_file_lines(file, flags);
+    } else {
+        head_file_chars(file, flags);
+    }
+}
+
+COMMAND(head) {
+    struct Flags flags;
+    flags.count = 10;
+    flags.lines = true;
+    flags.print_headers = false;
+    flags.dont_print_headers = false;
+
+    int start = 0;
+    for (int i = 0; i < argc; i++) { 
+        if (!prefix("-", argv[i])) break;
+        if (streql(argv[0], "--help")) help();
+        start++;
+        int i_s = i;
+        for (size_t j = 1; j < strlen(argv[i_s]); j++) {
+            char c = argv[i_s][j];
+            switch(c) {
+                case 'c': {
+                    start++;
+                    flags.lines = false;
+                    char* arg = next_arg(argc, argv, ++i);
+                    long int bkm = get_blkm(arg);
+                    if (bkm < 1) {
+                        error("error: bkm cannot be less than 1");
+                    }
+                    flags.count = bkm;
+                    break;
+                }
+                case 'n': {
+                    start++;
+                    flags.lines = true;
+                    char* arg = next_arg(argc, argv, ++i);
+                    long int bkm = get_blkm(arg);
+                    if (bkm < 1) {
+                        error("error: bkm cannot be less than 1");
+                    }
+                    flags.count = bkm;
+                    break;
+                }
+                case 'q':
+                    flags.dont_print_headers = true;
+                    break;
+                case 'v':
+                    flags.print_headers = true;
+                    break;
+                default: {
+                    error("error: unknown option -%c", c);
+                }
+            }
+        }
+    }
+
+    int count = argc - start;
+
+    if (count < 1) {
+        head_file_lines(stdin, &flags);
+        return EXIT_SUCCESS;
+    }
+
+    if (count == 1) {
+        head_file(argv[start], &flags, false);
+        return EXIT_SUCCESS;
+    }
+
+    for (int i = 0; i < count; i++) {
+        head_file(argv[start + i], &flags, true);
+    }
+
+    return EXIT_SUCCESS;
+}