I agree, FTP is not intuitive and would go as far as to say that it should not be part of any normal curriculum any more. Furthermore there are differences between active and passive FTP connections. Take a look at the sequence diagram for FTP. You can see how complicated it is from a packet filter perspective, as you are finding out first hand. Notice also how it was designed decades before packet filters became common, back when direct connections to the Internet itself were expected on both ends. Therefore FTP does not work well through NAT, for example.

yea also bash script for me all programming is hard, but especially bash scripting I don't understand how to create scripts that work

Like in any other programming, shell scripting is about taking it one small piece at a timeand then gradually putting the working pieces together.

There are a lot of good guides for shell scripting. Here are two:

• BashGuide
• The Linux Command Line, 5th edition, see Part 4 "Writing Shell Scripts".

(The book ought to be available at your library, but can otherwise be ordered inter-library loan or just plain bought. If none of those are an option, you can still make do with an CC-licensed PDF.)

Also, take advantage of the ShellCheck site to inspect your scripts.