The first one uses Bitcoin script to implement string concatenation in the stack? I did not find a valid opcode in the latest Bitcoin script?
There aren't any string concatenation OPs in bitcoin simply because there is no use cases for it in a payment system.
There used to be a couple of disabled OP codes in early version that are completely
removed now that use to deal with string manipulation: OP_CAT, OP_SUBSTR, OP_LEFT, OP_RIGHT
Second, how can I better learn the Bitcoin script, or can I recommend some good information?
I don't know any source that explains everything but chapter 7 of the book called "Mastering Bitcoin" has a good explanation of the standard scripts that should give you enough information about how things work:
https://github.com/bitcoinbook/bitcoinbook/blob/develop/ch07.asciidoc(You may want to start in chapter 6 where it explains transactions).
For additional information and details you should check the source code and then ask questions here about any part that is unclear:
https://github.com/bitcoin/bitcoin/blob/master/src/script/interpreter.cppI'm sorry .When I saw tapscript, I paid attention to this sentence: Many previously disabled opcodes are redefined to be OP_SUCCESS opcodes that unconditionally render the entire script valid to simplify soft fork upgrades. I don't quite understand what is the use of OP_SUCCESS opcodes? Could you explain that?