cat clone

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define BLANK_LINES 1
#define ALL_LINES   2

static char **parse_options(char *argv[]);
static void read_file(FILE *in);
static void version(void);
static void help(void);

static int control;    /* Show control characters as ^ */
static int show_count; /* Show line count */
static int show_end;   /* End lines with $ */
static int show_tab;   /* Show tabs as ^I */
static int squeeze;    /* Change multiple blank lines into one */

static int line = 1;

int main(int argc, char *argv[])
{
  argv = parse_options(argv);

  if (*argv == NULL) {
    read_file(stdin);
  } else {
    FILE *in;

    for (; *argv != NULL; *++argv) {
      if (**argv == '-') {
        in = stdin;
      } else {
        if ((in = fopen(*argv, "r")) == NULL) {
          continue;
        }
      }

      read_file(in);
    }
  }

  return 0;
}

char **parse_options(char *argv[])
{
  while (*++argv != NULL && **argv == '-') {
    /* Terminating options */
    if (strcmp(*argv, "--version") == 0) {
      version();
    }
    if (strcmp(*argv, "--help") == 0) {
      help();
    }

    /* Behavioral switches */
    while (*++(*argv) != '\0') {
      switch (**argv) {
        case 'b': show_count = BLANK_LINES;          break;
        case 'e': control = show_end = 1;            break;
        case 'n': show_count = ALL_LINES;            break;
        case 's': squeeze = 1;                       break;
        case 't': control = show_tab = 1;            break;
        case 'u': /* No-op for Unix compatibility */ break;
        case 'v': control = 1;                       break;
        case 'A': control = show_end = show_tab = 1; break;
        case 'E': show_end = 1;                      break;
        case 'T': show_tab = 1;                      break;
        default: /* Ignore unrecognized switches */  break;
      }
    }
  }

  return argv;
}

void read_file(FILE *in)
{
  int ch, last;

  for (last = '\n'; (ch = getc(in)) != EOF; last = ch) {
    if (last == '\n') {
line_count:
      if (show_count == ALL_LINES) {
        printf("%-5d", line++);
      } else if (show_count == BLANK_LINES && ch != '\n') {
        printf("%-5d", line++);
      }

      if (squeeze && ch == '\n') {
        if (show_end) {
          putchar('$');
        }
        putchar('\n');

        /* Ignore extra empty lines */
        while ((ch = getc(in)) != EOF && ch == '\n') {
          /* Do nothing */
        }

        if (ch == EOF) {
          break;
        } else {
          goto line_count; /* Print line # first */
        }
      }
    }

    if (show_tab && ch == '\t') {
      printf("^I");
    } else if (control && iscntrl(ch)) {
      putchar('^');
    } else if (show_end && ch == '\n') {
      printf("$\n");
    } else {
      putchar(ch);
    }
  }
}

void version(void)
{
  printf("cat clone v1.0\n");
  exit(EXIT_SUCCESS);
}

void help(void)
{
  printf("cat [-benstuvAET] [--help] [--version] [file...]\n");
  exit(EXIT_SUCCESS);
}