If you need to know the actual casing of the name, Win32::GetLongPathName( ) will give it to you on Win32:

print "$_ : ",  Win32::GetLongPathName( $_ ) for qw[ file filE FILE Fi
+le ];;
## In   Out
file :  fIlE
filE :  fIlE
FILE :  fIlE
File :  fIlE
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This is a core function on Win32.