$^O is MSWin32 under Windows (at least recent ones)... unfortunately, as Abigail points out above, using $^O turns out not to be a completely reliable way to determine whether the globbing behavior is safe. To take one simple example, some shells on MSWin32 (Cygwin bash) expand wildcards and others (MS-DOS) don't.

The thing is that I would like to be able to do something that Does What I Mean -- or more precisely, Does What A Potentially Naive User Means. I suspect that somebody who uses DOS/Win and is familiar with commands like copy *.txt \over_here would expect to be able to write munge *.txt and have it do what he'd expect, not report File not found: *.txt.

I suppose one kludgish approach would be to perform the globbing if ($filename =~ /[?*]/ && !-e $filename), for example. Since this particular munging process is non-destructive, there's probably no danger in trying to glob if and only if the filename passed in does not exist. (Yes, I realize that testing for /[?*]/ is a very DOS-centric approach because Unix shells may support more sophisticated wildcarding... this is just a "for example".)

Interesting that this turns out to be a harder problem to solve that it seemed at first. As Abigail says, the real answer is probably to use a globbing vs. a non-globbing shell. I was just hoping there would be a way to make the behavior essentially consistent across platforms and shells without requiring that much thought on the part of a user. (I guess that's what GUIs are for ;-)