Or:

my( $name, $ext );
{
  my @chunks = split/\./, $filename; 
  $ext = pop @chunks;
  $name = join '.', @chunks;
}
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If you don't like reverse for some reason.

Actually I really liked gryng's answer... I was just trying to thing of another way to do it using split.

For them that like one-liners:

my( $ext, $name )=(@_=split/\./, $filename and pop @_, join '.', @_);
[download]