Question

The tee command reads its standard input until end-of-file, writing a copy of the input to standard output and to the file named in its command-line argument. Implement tee using I/O system calls. By default, tee overwrites any existing file with the given name. Implement the -a command-line option (tee -a file), which causes tee to append text to the end of a file if it already exists. (Use the getopt() function or write your own to parse command-line options.)

Answer 1

1.

#include <stdio.h>

#include <stdlib.h>

#include <getopt.h>

static int append_mode =0;

int parse_args(int argc, char *argv[])

{

char c;

while ((c = getopt(argc, argv, "a")) != -1) {

switch (c) {

case 'a':

append_mode = 1;

break;

case '?':

if (isprint(optopt))

fprintf(stderr, "Unkonw option `-%c'.\n", optopt);

else

fprintf(stderr,

"Unknown option character `\\x%x'.\n", optopt);

return 1;

default:

abort();

break;

}

}

return 0;

}

int main(int argc, char *argv[])

{

char buf[100];

size_t len;

char *file_mode;

int i;

FILE *files[20];

int num_files;

if (parse_args(argc, argv)) {

return 1;

}

file_mode = (append_mode ? "a" : "w");

num_files = argc - optind;

if (num_files > 0) {

if (files == NULL) {

fprintf(stderr, "Unable to allocate file buffer space\n");

return 1;

}

/* go through file arguments and either open for writing

or append based on the -a flag */

for (i = optind; i < argc; i++) {

FILE *pFile = fopen(argv[i], file_mode);

if (pFile == NULL)

{

fprintf(stderr, "Unable to open file %s for mode %s",

argv[i], file_mode);

goto main_cleanup;

}

files[i - optind] = pFile; /* mind the offset */

}

}

FILE *not_stdin = fopen("tee.c", "r");

while ((len = fread(&buf[0], 1, sizeof(buf), not_stdin)) > 0) {

fwrite(&buf[0], 1, len, stdout);

for (i = 0; i < num_files; I++) {

fwrite(&buf[0], 1, len, files[i]);

}

}

main_cleanup:

if (num_files > 0) {

for (i = 0; i < num_files; i++) {

fclose(files[i]);

}

}

return 0;

}