Your /etc/hosts file lines 3 and 11 have zero or more white space characters and nothing else. You should skip those:

while (<FILE>) {
  next if /\A\s*\z/ ; # skip blank lines
  next if /^\s*#/ ; # skip comments
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Or combine the regexes:

  next if /\A\s*(?:#|\z)/ ; skip comments and blank lines
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