utils-std

yes.c (1750B)

// utils-std: Collection of commonly available Unix tools
// SPDX-FileCopyrightText: 2017 Haelwenn (lanodan) Monnier <contact+utils@hacktivis.me>
// SPDX-License-Identifier: MPL-2.0
#define _POSIX_C_SOURCE 200809L
#include <assert.h>
#include <errno.h>
#include <limits.h> // PAGESIZE
#include <stdio.h>  // perror
#include <string.h> // strlen
#include <unistd.h> // write
#ifndef PAGESIZE
// When undefined (allowed by POSIX), assume a somewhat modern system but not too modern
#define PAGESIZE 4096
// If getting a true pagesize is important then sysconf(_SC_PAGESIZE)
// should be used as it is more runtime than ABI.
// (for example AArch64 allows different pagesizes)
#endif
int
main(int argc, char *argv[])
{
	char *args = NULL;
	size_t args_len = 0;
	if(argc == 1)
	{
		static char str_yes[3] = {'y', '\n', '\0'};
		args = str_yes;
		args_len = 2;
	}
	else
	{
		argv++;
		argc--;
		args = *argv;
		for(int i = 0; i < argc; i++)
		{
			size_t len = strlen(argv[i]);
			argv[i][len] = ' ';
			args_len += len + 1; // str + space
		}
		if(args_len == 0)
		{
			static char str_nl[2] = {'\n', '\0'};
			args = str_nl;
			args_len = 1;
		}
		else
			argv[0][args_len - 1] = '\n';
	}
	size_t buflen = args_len;
	char *buf = args;
	// Large buffer to avoid write-speed being syscall-bound
	// PAGESIZE was chosen because yes(1) is likely going to be piped
	if(args_len < PAGESIZE)
	{
		static char page_buf[PAGESIZE] = "";
		buf = page_buf;
		size_t i = 0;
		do
		{
			memcpy(buf + i, args, args_len);
			i += args_len;
		} while(i < (PAGESIZE - args_len));
		buflen = i;
	}
	assert(errno == 0);
	while(write(STDOUT_FILENO, buf, buflen) >= 1)
		;
	if(errno != 0)
	{
		perror("yes: error: Failed writing");
		return 1;
	}
	return 0;
}