src/cat.c


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#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define error(...) ({ \
    printf(__VA_ARGS__); \
    exit(EXIT_FAILURE); \
    })

static void cat(char *s) {
  int fd = STDIN_FILENO;
  ssize_t in, out;
  char buf[1024];

  if(strcmp(s, "-")) {
    fd = open(s, O_RDONLY);
    if(fd < 0)
      error("Error opening %s: %s\n", s, strerror(errno));
  }

  for(;;) {
    in = read(fd, buf, sizeof(buf));
    if(in < 0)
      error("Error reading %s: %s\n", s, strerror(errno));
    out = write(STDOUT_FILENO, buf, in);
    if(out < in)
      error("Error writiing output: %s\n", strerror(errno));
    if(!in)
      return;
  }
}

int main(int argc, char **argv) {
  if(argc == 1) {
    cat("-");
    return 0;
  }

  while(argc-- > 1)
    cat(*(++argv));

  return 0;
}