echo <<<输出做什么? [重复]

This question already has an answer here:

I came across some code in a file I was working that basically has

echo <<<output

"some html here"

output;

What does this do? Normally I do something like

echo "some html here";

but I've run into some cases where I have to use both ' and " and then it breaks the statement to echo, I think the first method would be a way around this but I would like to know what it's actually doing.

Thanks in advance.

</div>

You are looking at heredoc notation.

A third way to delimit strings is the heredoc syntax: <<<. After this operator, an identifier is provided, then a newline. The string itself follows, and then the same identifier again to close the quotation.