How to make a string with base currency?

 
Hi I need help just obtaining a simple string that contains the 3 character base currency of the current symbol. Like for GBPJPY I want the string to be "GBP" for AUDUSD I want "AUD" -- I can think of a long way to do this, but there must be an easy way. Any help is appreciated. Thanks.
 
Thank you very much!
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