XX(1) General Commands Manual XX(1)

xx — hexdump

xx [-arsz] [-c cols] [-g group] [-p count] [file]

xx dumps the contents of a file or standard input in hexadecimal format.

The arguments are as follows:

Toggle ASCII output.
cols
Output cols bytes per line. The default cols is 16.
group
Output extra space after every group bytes. The default group is 8.
count
Output a blank line after every count bytes. count must be a multiple of cols.
Reverse hexdump. Read hexadecimal input and write byte output.
Toggle offset output.
Skip output of lines containing only zeros.

hexdump(1), xxd(1)

September 7, 2018 OpenBSD 7.4

xx.c in git 

/* Copyright (C) 2017  June McEnroe <june@causal.agency>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <ctype.h>
#include <err.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

typedef unsigned char byte;

static bool zero(const byte *ptr, size_t size) {
	for (size_t i = 0; i < size; ++i) {
		if (ptr[i]) return false;
	}
	return true;
}

static struct {
	size_t cols;
	size_t group;
	size_t blank;
	bool ascii;
	bool offset;
	bool skip;
} options = { 16, 8, 0, true, true, false };

static void dump(FILE *file) {
	bool skip = false;

	byte buf[options.cols];
	size_t offset = 0;
	for (
		size_t size;
		(size = fread(buf, 1, sizeof(buf), file));
		offset += size
	) {
		if (options.skip) {
			if (zero(buf, size)) {
				if (!skip) printf("*\n");
				skip = true;
				continue;
			} else {
				skip = false;
			}
		}

		if (options.blank) {
			if (offset && offset % options.blank == 0) {
				printf("\n");
			}
		}

		if (options.offset) {
			printf("%08zX:  ", offset);
		}

		for (size_t i = 0; i < sizeof(buf); ++i) {
			if (options.group) {
				if (i && !(i % options.group)) {
					printf(" ");
				}
			}
			if (i < size) {
				printf("%02hhX ", buf[i]);
			} else {
				printf("   ");
			}
		}

		if (options.ascii) {
			printf(" ");
			for (size_t i = 0; i < size; ++i) {
				if (options.group) {
					if (i && !(i % options.group)) {
						printf(" ");
					}
				}
				printf("%c", isprint(buf[i]) ? buf[i] : '.');
			}
		}

		printf("\n");
	}
}

static void undump(FILE *file) {
	byte c;
	int match;
	while (0 < (match = fscanf(file, " %hhx", &c))) {
		printf("%c", c);
	}
	if (!match) errx(1, "invalid input");
}

int main(int argc, char *argv[]) {
	bool reverse = false;
	const char *path = NULL;

	int opt;
	while (0 < (opt = getopt(argc, argv, "ac:g:p:rsz"))) {
		switch (opt) {
			break; case 'a': options.ascii ^= true;
			break; case 'c': options.cols = strtoul(optarg, NULL, 0);
			break; case 'g': options.group = strtoul(optarg, NULL, 0);
			break; case 'p': options.blank = strtoul(optarg, NULL, 0);
			break; case 'r': reverse = true;
			break; case 's': options.offset ^= true;
			break; case 'z': options.skip ^= true;
			break; default: return 1;
		}
	}
	if (argc > optind) path = argv[optind];
	if (!options.cols) return 1;

	FILE *file = path ? fopen(path, "r") : stdin;
	if (!file) err(1, "%s", path);

	if (reverse) {
		undump(file);
	} else {
		dump(file);
	}
	if (ferror(file)) err(1, "%s", path);

	return 0;
}