coreutils

// head.c, version 1.0.3

// OMKOV coreutils implementation of POSIX head

// Copyright (C) 2020, Jakob Wakeling

// MIT Licence

#include "util/error.h"

#include "util/optget.h"

#include <stdbool.h>

#include <stdint.h>

#include <stdio.h>

#define VERSION "1.0.3"

static struct lop lops[] = {

	{ "help",    ARG_NUL, 256 },

	{ "version", ARG_NUL, 257 },

	{ NULL, 0, 0 }

};

static uintmax_t limit = 10;

static bool      label;

static inline int head(const char *path);

static void hlp(void);

static void ver(void);

int main(int ac, char *av[]) { A0 = av[0];

	struct opt opt = OPTGET_INIT; opt.str = "n:"; opt.lops = lops;

	for (int o; (o = optget(&opt, av, 1)) != -1;) switch (o) {

	case 'n': {

		register uintmax_t d; register char *p = opt.arg;

		for (limit = 0; *p >= '0' && *p <= '9'; ++p) {

			d = (uintmax_t)*p - '0';

			if (limit > (UINTMAX_MAX - d) / 10) { break; }

			limit = limit * 10 + d;

		}

		if (*p) { error(1, "%s: invalid line count", opt.arg); }

		break;

	}

	case 256: { hlp(); return 0; }

	case 257: { ver(); return 0; }

	default: { return 1; }

	}

	bool warned = false;

	if (opt.ind == ac) { head("-"); return 0; }

	if (opt.ind + 1 != ac) { label = true; }

	for (char **p = &av[opt.ind]; *p; ++p) if (head(*p)) {

		warn("%s: %s", *p, serr()); warned = true;

	}

	return warned;

}

static inline int head(const char *file) {

	char stdbuf[BUFSIZ * 16]; FILE *fi;

	register uintmax_t l = 0;

	if (file[0] == '-' && file[1] == 0) { fi = stdin; }

	else if (!(fi = fopen(file, "r"))) { return 1; }

	if (label) { static bool spc = false;

		if (spc) { fputc('\n', stdout); } else { spc = true; }

		printf("==> %s <==\n", file);

	}

	if (limit == 0) { goto end; }

	for (size_t c; (c = fread(stdbuf, 1, sizeof (stdbuf), fi));) {

		for (register size_t i = 0; i != c; ++i) {

			fputc(stdbuf[i], stdout);

			if (stdbuf[i] == '\n' && ++l == limit) { goto end; }

		}

	}

end:

	if (fi != stdin) { fclose(fi); } return 0;

}

static void hlp(void) {

	puts("head - output the first part of files\n");

	puts("usage: head [-n number] [file...]\n");

	puts("options:");

	puts("  -n number  Number of lines to output for each file");

	puts("  --help     Display help information");

	puts("  --version  Display version information");

}

static void ver(void) {

	puts("OMKOV coreutils head, version " VERSION);

	puts("Copyright (C) 2020, Jakob Wakeling");

	puts("MIT Licence (https://opensource.org/licenses/MIT)");

}