Changing the spec it is, then. I can enforce a 'files must have no shell wildcard characters in their names' policy with this.

With that in mind, and after thinking over the problem some more, I came up with a test (update: the same test the ysth beat me to by 3 minutes) that seems to work:

if ( grep {-e} glob $file ) {...
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In this way, if $file is a single filename that doesn't exist, it will fail on the -e test. If $file is multiple files, glob will see them all.