The crypt function from unistd.h as a command.

crypt.c

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

int main(int argc, char **argv) {
  if (argc > 1) {
    if (argc > 2) {
      char salt[3];
      salt[0] = *argv[2];
      if (strlen(argv[2]) < 2)
        salt[1] = *argv[2];
      else
        salt[1] = argv[2][1];
      salt[2] = 0;
      printf("%.*s", 11, crypt(argv[1], salt) + 2);
      return 0;
    }
    else
      fputs("crypt: no salt given\n", stderr);
  }
  else
    fputs("crypt: no password given\n", stderr);
  return 1;
}