| 1 |
/\s0(1+)/ matches a "whitespace" character followed by a zero and one or more 1s -- the set of ones is stored in \1 (and $1)
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| 2 |
/[0-9]\.0\D/ matches "the answer is 1.0 exactly" but not "the answer is 1.00" because of \D
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In first case, $` is "the answer is ", $& is "1.0 " and $' is "exactly"
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| 3 |
/a.*c.*d/ matches "axxxxcxxxxcdxxxxd" with
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$` and $' as null and $& as full string (because greedy)
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| 4 |
/(a.*b)c.*d/ matches "axxxxbcxxxxbd" with
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\1 as "axxxxb" -- note backtracking as greedy (a.*b) first matches to "axxxxbcxxxxb" but then tries again when following c.*d fails to match
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