micro-utils/coreutils/echo.c

#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
// I want to perform some sort of hack using errno for flag passing

static char should_stop = 0;

char* ScreenString(const char* str) {
	size_t len = strlen(str);
	char* buf = malloc(len + 1);
	size_t i, buf_idx = 0;

	for(i = 0; i < len - 1; i++) {
		if (str[i] == '\\') {
			switch(str[i+1]) {
				case 'a':
					buf[buf_idx++] = '\a';
					break;
				case 'b':
					buf[buf_idx++] = '\b';
					break;
				case 'c':
					buf[buf_idx] = '\0';
					should_stop = 1;
					return buf;
				case 'f':
					buf[buf_idx++] = '\f';
					break;
				case 'n':
					buf[buf_idx++] = '\n';
					break;
				case 'r':
					buf[buf_idx++] = '\r';
					break;
				case 't':
					buf[buf_idx++] = '\t';
					break;
				case 'v':
					buf[buf_idx++] = '\v';
					break;
				case '\\':
					buf[buf_idx++] = '\\';
					break;
				case '0':
					unsigned int c = 0;
					int offset = 0;
					if (sscanf(str + i + 1, "%3o%n", &c, &offset)) {
						buf[buf_idx++] = c;
						i += offset;
					}
					break;
				default:
					buf[buf_idx++] = '\\';
					continue;
			}
			i++;
		} else {
			buf[buf_idx++] = str[i];
		}
	}

	if (i < len) buf[buf_idx] = str[i];
	errno = 0;
	return buf;
}

int main(int argc, const char **argv) {
	char newline = 1;

	if (argc > 1) {
		if (strcmp(argv[1], "-n") == 0) {
			newline = 0;
			argv++;
			argc--;
		}

		for (int i = 1; i < argc; i++) {
			char* screened = ScreenString(argv[i]);
			fputs(screened, stdout);
			free(screened);
			if (should_stop) return 0;
			if (i < argc - 1)
				putchar(' ');
		}
	}
	/* https://pubs.opengroup.org/onlinepubs/009604599/utilities/echo.html */
	/* This version does not support -n option and escape-sequences */
	/* https://gist.github.com/fogus/1094067/ */
	/* It seems like escape sequences are supported only by GNU's one */
	/* I'd implemented them anyway but you may like not to include them */
	/* Or to switch them with a flag */

	if (newline)
		putchar('\n');
	return 0;
}