Question

I noticed that Feedzirra uses this regex to get the ETag from response header:

/.*ETag:\s(.*)\r/

Personally I would have written this one:

/ETag:\s(.*)\n/

Here the questions:

1. Why does it put .* at the beginning even if it is unnecessary (\A is not specified)?
2. Why does it use \r instead of \n? What is the difference?

Answer 1

1. Completeness I dare say. It’s not part of a capture. There may be an implicit start of line anchor though, depending on language and implementation, and in this case it may be necessary.
2. The HTTP spec says that HTTP is to use "\r\n" as a line ending. In most programming languages, only "\n" is treated as a line ending. The \r makes sure that the \r is not swallowed inside the .* which would give erroneous whitespace at the end of the capture.