replace-tab-with-space.c

/* Copyright © 2021-2023 Chee Bin HOH. All rights reserved.
 *
 * Replace tab with space, and we can potentially do this in awk than
 * a C program.
 *
 * We assume a tab is equivalent to 8 spaces, but it is not always the
 * case.
 */

#include <ctype.h>
#include <libgen.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int space2Tab = 8;
char *programName = NULL;

void printHelp(void) {
  fprintf(stderr, "%s [-h] [-t space]\n", programName);
  fprintf(stderr, "\n");
  fprintf(stderr, " -h       : print this help message\n");
  fprintf(stderr, " -t space : number of space per tab [default is 8 and must "
                  "be 1 or above]\n");
}

int main(int argc, char *argv[]) {
  int c;
  int i;
  int startWithNoneSpace = 0;

  programName = basename(argv[0]);

  while ((c = getopt(argc, argv, "ht:")) != -1) {
    switch (c) {
    case 't':
      space2Tab = strtol(optarg, NULL, 0);
      break;

    case '?':
    case 'h':
      printHelp();
      exit(1);
    }
  }

  if (space2Tab <= 0) {
    printHelp();
    exit(1);
  }

  while ((c = getchar()) != EOF) {
    if ('\t' == c && !startWithNoneSpace) {
      for (i = 0; i < space2Tab; i++)
        putchar(' ');
    } else {
      if (!isspace(c))
        startWithNoneSpace = 1;
      else if ('\n' == c)
        startWithNoneSpace = 0;

      putchar(c);
    }
  }

  return 0;
}