I want to get the sub string like "%AE%3D%5B" from a long string file:///qwert%AE%3D%5BXXXXX, the sub string length is not fixed, the chars is a HEX between two "%", how to get the %HEX%HEX%HEX%HEX... from a string using regex? thank you,

Not sure of what range of characters you are trying to match but if you are trying to match a string of % followed by 2 non-% chars, one or more times:

(?:%[^%]{2})+

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Thank you very much, it works well!