C-Code

/********************************************
 * pwgen.c    password generator
 ********************************************/
#include <unistd.h>
#include <stdlib.h>
#include <stdbool.h>
#include <stdio.h>
#include <ctype.h>
#include <time.h>

#define MAX_LETTERS ('Z'-'A'+1)
#define MAX_NUMBERS ('9'-'0'+1)
#define MIN_PWLEN 5
#define DEF_PWLEN 8
#define MAX_PWLEN 255

short special_chars[] = {33,35,36,37,38,42,43,45,46,47,\
                         58,59,61,63,91,92,93,94,95,126};
int max_special = sizeof(special_chars) / sizeof(short);

bool opt_lower = false;
bool opt_upper = false;
bool opt_digit = false;
bool opt_special = false;

/*** functions ***/
// usage
void usage_exit(int exit_code) {
  printf(
"Usage: pwgen [-aAns] [Länge]\n"
"       -a : Kleinbuchstaben\n"
"       -A : Großbuchstaben\n"
"       -n : Ziffern\n"
"       -s : Sonderzeichen\n"
"    Länge : Passwortlänge (Default %d)\n", DEF_PWLEN);
  exit(exit_code);
}

// prepare password character set
// returns number of characters in set
int set_pwchars(char *charset) {
	int c, p;
	
    p = 0;
	if (opt_lower)
		for (c='a'; c<='z'; c++,p++)
			charset[p] = c;	
	if (opt_upper)
		for (c='A'; c<='Z'; c++,p++)
			charset[p] = c;	
	if (opt_digit) {
		for (c='0'; c<='9'; c++,p++)
			charset[p] = charset[p+MAX_NUMBERS] = c;
		p += MAX_NUMBERS;
	}
	if (opt_special)
		for (c=0; c<max_special; c++,p++)
			charset[p] = special_chars[c];
	return p;
}

// generate password
// returns pointer to password string
//  pwchars: password character set (array)
//    pwmax: length of character set
//    pwlen: length of password string
char *gen_password(char *pwchars, int pwmax, int pwlen) {
	static char passwrd[MAX_PWLEN+1];
	int clower, cupper;
	int cdigit, cspecial;
	int c, p;
	bool pwok = false;
	
	// generate PW
    if (pwlen < MIN_PWLEN) pwlen = MIN_PWLEN;
    if (pwlen > MAX_PWLEN) pwlen = MAX_PWLEN;
    
	while (!pwok) {
		clower = cupper = cdigit = cspecial = 0;
		srandom(time(NULL));
		// fill array with random characters
		for (p=0; p<pwlen; p++) {
			c = pwchars[ (random() * pwmax/RAND_MAX) ];
			if (islower(c)) 
				clower++;
			else if (isupper(c)) 
				cupper++;
			else if (isdigit(c))
				cdigit++;
			else
				cspecial++;
			passwrd[p] = c;
		}
		// check password characters
		if ((opt_lower && clower == 0) ||
		    (opt_upper && cupper == 0) ||
		    (opt_digit && cdigit == 0) ||
		    (opt_special && cspecial == 0))
				continue;
		pwok = true;			
	}
	passwrd[pwlen] = '\0';
	return passwrd;
}

/*** main ***/
int main(int argc, char **argv) {
	char pwch[2*(MAX_LETTERS + MAX_NUMBERS) + max_special];
	int opt, pwlen;

    // get password options [-aAns] [length]
    while ((opt = getopt( argc, argv, "aAnsh" )) != -1) {
      switch(opt) {
          case 'a': opt_lower = true; break;
          case 'A': opt_upper = true; break;
          case 'n': opt_digit = true; break;
          case 's': opt_special = true;	break;
          case 'h': usage_exit(EXIT_SUCCESS); break;
          default : usage_exit(EXIT_FAILURE);
      }
    }
    pwlen = (argc-optind > 0) ? atoi(argv[optind]) : DEF_PWLEN;
	if ((opt_lower | opt_upper | opt_digit | opt_special) == 0)
		opt_lower = true;

	printf("%s\n", gen_password(pwch, set_pwchars(pwch), pwlen));
	return 0;
}