This syntax works pretty much as I would expect, opening the next file returned by the glob each time the subroutine is called. However, you're still going to have a problem, because no matter what you will run out of files, glob will return undef, the open will fail, and your script will die.

You should probably be doing something more like this:

sub foo {
  defined($file = <abc*>) or return;
  open(FH, $file) or die $!;
  ...
}
[download]

However, I suspect that you may be creating the files after you have executed the glob the first time. perlop explains why this won't work as you intend:

       A glob evaluates its (embedded) argument only when it is
       starting a new list.  All values must be read before it
       will start over.  In a list context this isn't important,
       because you automatically get them all anyway.  In scalar
       context, however, the operator returns the next value each
       time it is called, or a undef value if you've just run
       out.
[download]

If that's the issue, you should not be using glob; you should keep track of the files when you create them, pulling the names from an internal list rather than globbing the file system.

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