Need help with a regex pattern for matching part of word until next uppercase letter

I need part of a word. For e开发者_如何学运维xample if we have "CheckResults" I just want to get "Check". Can someone help me with regex for this?

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\b[A-Z][a-z]+

Finds the begining of a word and then matches until the end of the word or a capital letter. If the word won't always be capitalized, use this:

\b[A-Z]?[a-z]+