önskas: fil med alla symboler längd 1-6

h@0xEBFE:/tmp$ gcc -lm a.c
h@0xEBFE:/tmp$ time ./a.out > a

real    0m1.705s
user    0m1.520s
sys     0m0.160s
h@0xEBFE:/tmp$ wc -l a
7529537 a

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <math.h>

#define WORD_LENGTH 6

int main(int argc, char *argv[])
{
    char charset[] = "abcdABCD012345";
    char word[WORD_LENGTH + 1];
    size_t charset_size;
    double number_of_words;
    unsigned int i,j,k,char_number;

    charset_size = strlen(charset);
    number_of_words = pow(charset_size, WORD_LENGTH);
    memset(word,0, WORD_LENGTH + 1);

    for(i=0; i<=number_of_words; i++)
    {
        k = i;
        for(j=0; j<WORD_LENGTH; j++)
        {
            char_number = k % charset_size;
            word[j] = charset[char_number];
            k /= charset_size;
        }
        printf("%s\n", word);
    }

    return 0;
}

#include <stdio.h>

void
generate (char charset[], int length, char word[])
{
  int i;
  
  if (length == 0)
    puts (word);
  else
    {
      for (i = 0; charset[i] != 0; i++)
        {
          word[length-1] = charset[i];
          generate (charset, length-1, word);
        }
    }
}

int
main (void)
{
  int length = 6;
  char charset[] = "abcdABCD012345";
  char word[length+1];
  word[length] = 0;

  generate (charset, length, word);

  return 0;
}

$ cc gen.c
$ time ./a.out > output

real	0m0.372s
user	0m0.210s
sys	0m0.083s
$ wc -l output
7529536 output