And here's why this is the best choice at the time I wrote it: require is faster than eval STR. In addition, Win32::DriveInfo (according to its documentation) doesn't export anything anyway.

Personally, I use require over use more that most people here, it seems - but fully qualified names don't bother me as they do some.

Alternately, you could just always load Win32::DriveInfo:

my $hasdriveinfo = eval { require Win32::DriveInfo; 1 };
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This will fail gracefully on Unix, but load the module on Windows. The only downside is if Win32::DriveInfo isn't installed on Windows, and you absolutely must use it on Windows. Then you'll need to check:

if ($^O eq 'MSWin32' and not $hasdriveinfo)
{
  die "failed to load Win32::DriveInfo - is it installed? $@";
}
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At this point, jbrugger's answer is way simpler, if you do really need it.