Good day, everyone!
I've started using/learning UNIX recently and the only problem i get, is that I can hardly edit a file from within the script (searching/replacing, extracting, ect.) I've tried vi, ex, ed all of them did only half of job, which means they opened out a file but did not perform any editing or any required operations. Hence, I've got a question:
which editor do i need to use, to be able to perform an editing of a file from the script?

Thank you very much for any suggestions and what's more important explanations

ex/sed/awk are your friends

What type of problem you have encountered with 'vi' ?

The main problem i'm having with vi is, that i understand how to open a file on specific line, the thing I don't get is how to save the changes. For example, I've been trying to do something like this.
As I said, it only opened editor in Insert mode.
It's probably silly me
I've tried to use sed, and it helped, although that was the code I've found on Internet, but I don't understand completely the meaning of criterias yet.
p.s. I've managed to solve the given example using temp file, which is being an absolutely time and space consuming solution....

You can simply do whatever you want with test in ed/sed/awk etc.
Notice that, you can edit content of file during reading it and forward output from it to other file and after that simple overwrite it e.g. in awk:
Or use ed like it:
depends from your expectations.

Thank you very much. That's helped a lot!