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<?php $a = "bla blah dfkjd fkdh fkd fks sdkf skdfh djfh [br] [BR] [BR]asdsadhjasjidsahjhsahiasdhi"; echo preg_replace('!\[br\](\s+\[br\])+!i', 'INSERT$0', $a);
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bla blah dfkjd fkdh fkd fks sdkf skdfh djfh INSERT[br] [BR] [BR]asdsadhjasjidsahjhsahiasdhi