If there is no tax expression, it is not familiar with this term and concept. However, they are not so nice you imagine. Recall how to find files on the hard disk. You will definitely use the * characters to help find the files you are looking for. • Characters match a single character in the file name, and * matches one or more characters. A pattern such as 'data ?dat' can find the following file: Data1.dat Data2.dat DataX.dat Datan.dat If you use * characters instead? The number of files will be expanded. 'data * .dat' can match all the following file names: data.dat data1.dat data2.dat data12.dat Datax.dat Dataxyz.dat Although this search file is definitely useful, it is also very limited. • The limited capacity of wildcards can make you have a concept of regular expressions, but the regular expression is more powerful, and more flexible.
