Understanding ruby quine
heredoc, quine, ruby
Solution
The `<<something` syntax begins a here-document, borrowed from UNIX shells via Perl - it's basically a multiline string literal that starts on the line after the `<<` and ends when a line starts with `something`.
So structurally, the program is just doing this:
puts str*2,2
... that is, print two copies of `str` followed by the number 2.
But instead of the variable `str`, it's including a literal string via a here-document whose ending sentinel is also the digit 2:
puts <<2*2,2
puts <<2*2,2
2
So it prints out two copies of the string `puts <<2*2,2`, followed by a 2. (And since the method used to print them out is `puts`, each of those things gets a newline appended automatically.)
Problem
I have found this code block on Wikipedia as an example of a quine (program that prints itself) in Ruby. ``` puts <<2*2,2 puts <<2*2,2 2 ``` However, I do not get how it works. Especially, what I do not get is that when I remove the last line, I get this error: syntax error, unexpected $end, expecting tSTRING_CONTENT or tSTRING_DBEG or tSTRING_DVAR or tSTRING_END What happens in those lines?