Special characters in Perl

\ W matches a letter, number, or underline, it is equivalent to [a-zA-Z_0-9] \ s matching an empty character \ D matching a number \ B matching the beginning and end of a word ^, $ is the unit of action to lock the location, while \ B locks the locations in the unit of words. These modifiers are in uppercase for the opposite situation. In this way, we can use \ W + to match a continuous string to match a word with \ B \ W + \ B to match a blank space and use \ s + to match all characters with [\ D]. match All characters except line breaks with ". "What is the difference between the suffix modifier/s and/m in Perl regular expressions? M is to process the string as multiple rows, S is to process the string as a single row, if s appears in the string \ n is equivalent to a common character. When the handle in <> is short for time, the default value is stdin, that is, the standard input, indicating that the data is obtained from the standard input (for example, using the keyboard input in the command line) while (<>) {} Read all specified files in @ argv (saving program running parameters), each row. If this parameter is not specified, the system reads data from the standard input by row and loops until the end.