I have the following command:
wash -n <groups> <<EOF echo hi echo bye <<BYE <commands> exit 0 BYE exit 0 EOF <commands> where <groups> are some groups and <commands> are commands. I don't understand what <<EOF and <<BYE mean? Is it some label which the script jumps in case fails? What does this script do?
It is a feature named "here document". Basically it means that the text between <<whatever and whatever are presented to the standard input of the command. In your case, the stdin seen by the first command is,
echo hi echo bye <<BYE <commands> exit 0 BYE exit 0 
<commands> is echo inside, I get hi and the bye. It does not run the command echo inside. Not sure I understood the flow. echo does not read from its standard input stream. The contents of the here-document is simply discarded. tl;dr: command << TEXT: the string TEXT is treated as end-of-file.
I tested, and it seems to be like this: When you do:
% command << TEXT csh reads the standard input, and when it catches TEXT, the full stdin before TEXT is redirected to command. (TEXT has to be on a separate row to work)
stdinalongside the command in a script.