It seems File::Glob::glob only uses the :nocase when there are some wildcards to match, otherwise it tries to find the name case insensitive, and when it fails, it returns the pattern itself. Using glob without any wildcards is therefore useless. You can, though, make the filename into a pattern by just turning its last character into a character class:

my @f = glob '/someDir/someFil[e]';
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My testing shows this behaviour is per node name, i.e. if you're not sure about the case of someDir, you need to change it to someDir, too.

See Path::Tiny for much nicer interface to file structure.