I'll give a quick breakdown here. Refer to perlre for details (I've indicated the appropriate sections).

• You were originally missing your first line because it was https and you'd only specified http. The s? means zero or more 's's (see Quantifiers).
• \S+? says match all non-whitespace non-greedily which stops it capturing the terminal period if it exists (further down under Quantifiers).
• [.] stops '.' being a special (match anything) character by placing it in a character class (see Metacharacters).
• [.]? just says zero or one non-special '.' (that's Quantifiers again).
• \s at the end anchors the URL (and optional '.') to the whitespace that follows it (see Character Classes and other Special Escapes).

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