(This will take input from STDIN and go to STDOUT). Depends on how you define blank lines. If you just want to remove lines that contain absolutely nothing, this will do the trick:

  while (<STDIN>)
    {
      print if (!/^$/);
    }
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^ and $ are anchors and indicate the start and end of the current record (which will be the current line with the default record seperator). If you mean to delete lines that only contain whitespace, this will do the trick:

  while (<STDIN>)
    {
      print if (!/^\s*$/);
    }
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(\s is the whitespace character, and includes newlines, spaces and tabs)

Andrew.