popen password change linux

Question

I try to change the password for an user on a linux system. I opened a pipe for this. Works great, except the user enters passwords that are treated as "weak" (I handle the case that the password is to short). On the terminal this prints a warning and then you have to re-enter the password to verify.

Here are the few lines of code (i stripped all the parts that are not relevant).

fp = popen("passwd myuser", "w");
fprintf(fp, "%s\n", newPw);
fprintf(fp, "%s\n", newPw);
status = pclose(fp);

How can I handle the new case, or is there a more elegant way to deal with password changes I am not aware of?

Answer 1

just added another fprintf(fp, "%s\\n", newPw) to handle the additional verification. If everything runs fine and the password is accepted as is, the additional print in the pipe is no problem...