if ($_ =~ /^S\s+[-]*\d+[\.\d+]*\s+[-]*\d+[\.\d+]*\s*\(\s*IOPUT|OUTPUT\s*\)/i)
  {
    print "PRE=$`\nMATCH=$&\nPOST=$'\nIt matches with case insensitive...\n";
  }

##</code><code>##

PRE=  onn (bbcreccsnnl_
MATCH=output)
POST= !OUTPUT
It matches with case insensitive...