A method and a system for efficient search of string patterns characterized by positional relationships in a character stream are disclosed. The method is based on grouping string patterns of a dictionary into at least two string sets and performing string search processes of a text of the character stream based on individual string sets with the outcome of a search process influencing a subsequent search process. A system implementing the method comprises a dictionary processor for generating string sets with corresponding text actions and search actions, a conditional search engine for locating string patterns belonging to at least one string set in a text according to a current search state, a text operator for producing an output text according to search results, and a search operator for determining a subsequent search state.