What is EOF!! in the bash script?

Question

There is a command I don\'t understand:

custom_command << EOF!!

I want to ask what EOF!! is in the bash script. I did find EOF with googl

Answer 1

As others already wrote, this is a here-document.

The token used for that should be chosen carefully; as the probability that the here-document contains EOF!! is lower than for EOF itself, they chose that.

I suppose they checked it does not harm before using it; !! in a script does NOT refer to the history, but it stays as it is.