cat.c

   1 /* `cat.c` - con*cat*enate and print files
   2    Copyright (c) 2022, Alan Potteiger
   3    See `LICENSE` for copyright and license details */
   4
   5 #define _POSIX_C_SOURCE 200809L
   6
   7 #include <stdio.h>
   8 #include <stdlib.h>
   9 #include <string.h>
  10 #include <errno.h>
  11 #include <unistd.h>
  12
  13 /* usage: cat [-u] [file...] */
  14
  15 int
  16 main(int argc, char *argv[])
  17 {
  18         FILE *in;
  19         int uflag;
  20         char ch;
  21
  22         argc--;
  23         argv++;
  24
  25         if (argc < 1)
  26                 goto noarg;
  27
  28         /* -u? */
  29         if (argv[0][0] == '-' && argv[0][1] == 'u') {
  30                 uflag = 1;
  31                 /* disable buffering for stdout, if the request cannot be
  32                    honored we'll print a brief message to stderr and continue
  33                    regular execution */
  34                 if (setvbuf(stdout, NULL, _IONBF, 0) == EOF)
  35                         fputs("cat: -u: unbuffer request failed\n", stderr);
  36                 argc--;
  37                 argv++;
  38         }
  39
  40         /* interpret remaining arguments as files to be read and printed */
  41         for (; argc != 0; argc-- && argv++) {
  42                 if (*argv[0] == '-')
  43                         in = stdin;
  44                 else
  45                         in = fopen(argv[0], "r");
  46
  47                 if (in == NULL) {
  48                         fprintf(stderr, "cat: %s: %s\n", argv[0],
  49                                         strerror(errno));
  50                         continue;
  51                 }
  52
  53                 /* disable buffering for our input stream, if the request
  54                    cannot be honored we'll print a brief message to stderr and
  55                    continue regular execution */
  56                 if (uflag) {
  57                         if (setvbuf(in, NULL, _IONBF, 0) == EOF)
  58                                 fputs("cat: -u: unbuffer request failed\n",
  59                                                 stderr);
  60                 }
  61
  62                 while ((ch = fgetc(in)) != EOF)
  63                         putchar(ch);
  64
  65                 fclose(in);
  66         }
  67
  68         return 0;
  69
  70 noarg:
  71         if (argc < 1) {
  72                 while ((ch = getchar()) != EOF)
  73                         putchar(ch);
  74         }
  75
  76         return 0;
  77 }
  78