utils

tee.c (1962B)

// Collection of Unix tools, comparable to coreutils
// SPDX-FileCopyrightText: 2017-2022 Haelwenn (lanodan) Monnier <contact+utils@hacktivis.me>
// SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only
#define _POSIX_C_SOURCE 200809L
#include <assert.h> /* assert() */
#include <errno.h>  /* errno */
#include <stdio.h>  /* fprintf(), fgetc(), fputc(), fclose(), fopen() */
#include <stdlib.h> /* malloc(), free(), abort() */
#include <string.h> /* strerror() */
#include <unistd.h> /* getopt(), opt… */
void
cleanup(FILE **fds)
{
	if(fds != NULL)
	{
		free(fds);
	}
}
int
main(int argc, char *argv[])
{
	const char *mode = "w";
	FILE **fds       = {NULL}; // Shut up GCC
	int c;
	while((c = getopt(argc, argv, ":ai")) != -1)
	{
		switch(c)
		{
		case 'a':
			mode = "a";
			break;
		case 'i': /* ignore SIGINT */;
			break;
		}
	}
	argc -= optind;
	argv += optind;
	if(argc > 0)
	{
		fds = malloc(sizeof(FILE *) * (size_t)argc);
		if(!fds)
		{
			fprintf(stderr, "Cannot allocate fd array: %s\n", strerror(errno));
			return 1;
		}
	}
	for(int argi = 0; argi < argc; argi++)
	{
		assert(argv[argi]);
		// POSIX: implementations shouldn't treat '-' as stdin
		fds[argi] = fopen(argv[argi], mode);
		if(fds[argi] == NULL)
		{
			fprintf(stderr, "Error opening ‘%s’: %s\n", argv[argi], strerror(errno));
			cleanup(fds);
			return 1;
		}
	}
	// main loop, note that failed writes shouldn't make tee exit
	int err = 0;
	while((c = fgetc(stdin)) != EOF)
	{
		if(fputc(c, stdout) == EOF)
		{
			fprintf(stderr, "Error writing ‘<stdout>’: %s\n", strerror(errno));
			err   = 1;
			errno = 0;
		}
		for(int argi = 0; argi < argc; argi++)
		{
			if(fputc(c, fds[argi]) == EOF)
			{
				fprintf(stderr, "Error writing to argument %d: %s\n", argi, strerror(errno));
				err   = 1;
				errno = 0;
			}
		}
	}
	// cleanup
	for(int argi = 0; argi < argc; argi++)
	{
		if(fclose(fds[argi]) != 0)
		{
			abort();
		}
	}
	cleanup(fds);
	return err;
}