1. Wild cards are typically a question mark (?), pound sign (#), or asterisk (*) used as placeholder symbols to stand in for letters.
典型的通配符是，问号（？） ，井号（#），或者星号（*），用来作为替代字母的占位符。
来自互联网
2. The inner for loop enumerates all the files in the current working directory -- the wild card * (asterisk) matches everything -- and then tests whether each entry is a file.
3. The inner for loop enumerates all the files in the current working directory -- the wild card * (asterisk) matches everything -- and then tests whether each entry is a file.
