Challenges

Extract every double-quoted string, including its quotes, where a backslash escapes the next character.

Extract every white bishop that is giving check along a diagonal, in board order.

A Sudoku box, flattened. Extract every digit that appears again later in the box.

Extract every number that is not immediately followed by "px".

Extract every number that is not a dollar amount — that is, not preceded by a $.

Extract the amounts that are prefixed with £ — and not the £ itself.

Extract every run of 1 to 4 digits — but never a fragment of a longer number.

Extract the fields of a CSV row, where a quoted field may contain commas. Quoted fields keep their quotes.

From a config file, extract every whole line that is commented out — every line beginning with a #. Inline comments on the end of a real setting do not count.

Extract "cat" only where it stands as a whole word.

Extract every http and https URL from a block of text, and nothing else that looks like a scheme.

Extract every run of five or more lower-case letters.

Pull out every lower-case vowel, in order.