grep2.c

#define _GNU_SOURCE

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <assert.h>

const char* const ANSI_COLOR_RED = "\x1b[31m";
const char* const ANSI_COLOR_RESET = "\x1b[0m";

const size_t BUFFERGROWTH = 128;


size_t getline_(char **lineptr, size_t *linesize, FILE *stream)
{
    if (*lineptr == NULL) {
        *lineptr = malloc(BUFFERGROWTH);
        *linesize = BUFFERGROWTH;
    }
    size_t buffer_i = 0;
    char c = 0;
    while (c != '\n') {
        // Detect need for buffer growth
        if (buffer_i >= *linesize) {
            *linesize += BUFFERGROWTH;
            *lineptr = realloc(*lineptr, *linesize);
        }
        c = getc(stream);
        if (c == -1) { // EOF
            break;
        }
        (*lineptr)[buffer_i++] = c;
    }
    (*lineptr)[buffer_i] = '\0';
    return buffer_i;
}

int main(int argc, char **argv)
{
	//TODO: create self-made strstr() function just for fun
	char *search_pattern;
	char *(*search_func)(const char*, const char*);

	if (argc == 2) {
		search_func = strstr;
		search_pattern = argv[1];
	} else if (argc == 3 && strcmp(argv[1], "-i") == 0) {
		search_func = strcasestr;
		search_pattern = argv[2];
	} else {
		fprintf(stderr, "Usage: grep [OPTION] [PATTERN]\n");
		return EXIT_FAILURE;
	}

	FILE *fp = stdin;
    size_t pattern_size = strlen(search_pattern);

    char *linebuffer = NULL;
    size_t linesize;
    size_t buffersize;

	while (linesize = getline_(&linebuffer, &buffersize, fp)) {
        char *search_start = linebuffer;
        while (1) {
            char *search_res = search_func(search_start, search_pattern);
            if ((search_start == linebuffer) && search_res == NULL) {
                // Skip line
                break;
            }
            if (search_res == NULL) {
                // Write remaining part of the line
                size_t size_remain = linebuffer + linesize - search_start;
                fwrite(search_start, 1, size_remain, stdout);
                break;
            }
            // Write non-matching part
            fwrite(search_start, 1, search_res - search_start, stdout);
            printf(ANSI_COLOR_RED);
            // Write matching part
            fwrite(search_res, 1, pattern_size, stdout);
            printf(ANSI_COLOR_RESET);

            search_start = search_res + pattern_size;
		}
	}

    return 0;
}