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)");
}