Slight mod to avoid leading space and need for capture. Puts a space (" ") instead of a tab. "\b" is not a space but a boundary.

perl -pi -e 's/(?!\A)(?=\p{IsUpper})/ /g'

In reply to Re: Editing File In-Place to put tab before UpperCase Letters by Your Mother
in thread Editing File In-Place to put tab before UpperCase Letters by ranjan_jajodia

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