What does f.write << TEMPLATE mean in the below code snippet

Question

File.open("db/quotes/#{id}.json", "w") do |f|
          f.write <<TEMPLATE
          {
            "submitter": "{hash["submitter"]}",
            "quote": "{hash["quote"]}",
            "attribution": "{hash["attribution"]}"
          }
          TEMPLATE
end

I understand what this method is doing. I read this code snippet out of a book. It is trying to write to a json to a file with whatever name #{id}.json is. I have never seen it before. Is "<<" an operator? What is "TEMPLATE"? Btw, this it out of the book rebuilding ruby on rails. In the section of rebuilding the Model layer is where i found the code snippet. It could have something to do with the Gem "erubis".

Answer 1

f.write expects a string as an argument and writes that string to the file f .

<<TEMPLATE starts a string that ends at the next occurrence of TEMPLATE . This kind of strings are called heredocs .

Answer 2

It's here-document syntax for string. It's a way to represent a string spanning multiple lines and the indentation will be preserved.

str = <<EOF
this will be the content
of your string
EOF

You can choose whatever word you want where I put EOF.

Answer 3

The other answers point you in the right direction of heredocs .

Technically this is syntax error with the string never terminating.

begin
  str = <<EOS
    This is my string
    EOS
end

Because the EOS at the beginning of the line. The below example works:

begin
  str = <<EOS
    This is my string
EOS
end

To have correctly indented code you would do the following:

begin
  str = <<-EOS
    This is my string
  EOS
end