Embodiments relate to generating a retrieval condition for retrieving a target character string from texts by pattern matching. An aspect includes dividing a first text into words. Another aspect includes generating a converted character string by performing at least one of appending at least one character in at least either one of previous and subsequent positions of the target character string. Another aspect includes replacing at least one character of the target character string. Another aspect includes generating the retrieval condition for retrieval candidates in the words of the first text, the retrieval condition comprising determining that a retrieval candidate matches the target character string and does not match the converted character string based on a ratio of a part of the retrieval candidate which matches the converted character string and corresponds to the target character string is less than or equal to a reference frequency.