We can use another form of variable expansion to select a specific substring, based on a specific character offset and length. Try typing in the following lines under bash.

可以根据特定字符偏移和长度，使用另一种形式的变量扩展，来选择特定子字符串。

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In respect to the limitation of document similarity measuring based on VSM, this paper put forward an algorithm based on public substring of strings.

针对向量空间模型在文档相似度量方面的局限，提出了基于计算公共子串的文档相似度量算法。

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Searches for the specified substring and returns the zero-based index of the last occurrence within the entire source string.

搜索指定的字符，并返回整个源字符串内最后一个匹配项的从零开始的索引。

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