echo "$root_passwd" | su -c "echo '$new_root_passwd' | passwd --stdin root"
echo "$weihu_passwd" | sudo -S bash -c "echo '$new_root_passwd' | passwd --stdin root"

其他方法参考：

newpasswd=bm4A3X@e
encrypted_passwd=$(openssl passwd -1 "$newpasswd")
usermod -p "$encrypted_passwd" root

[root@localhost ~]# passwd root << EOF
> passwd
> passwd
> EOF
Changing password for user root.
New password: Retype new password: passwd: all authentication tokens updated successfully.