找到指定字符串位置：

k = strfind(str,pat)

示例：

str = 'Find the starting indices of substrings in a character vector';

k = strfind(str,'in')

k = 1×5

     2    15    19    36    41

拆解文件名（除去后缀）

str = filename;
pat = '_';
newStr = extractBefore(str,pat);