I think you want (untested): 
s/([^\x00-\xFF])/sprintf "&#x%x;", $1/eg;  # Encode
s/&#x(\p{AHex}+);/chr hex $1/eg;           # Decode

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In reply to Re: sring encode problem (hexadecimal) by JavaFan
in thread sring encode problem (hexadecimal) by courierb

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