regex - Grep 正则表达式

Question

考虑这个文本文件:

TEST FILE : test                         #No match
                                         #No match
Run grep "1133*" on this file            #Match
                                         #No match
This line contains the number 113.       #Match
This line contains the number 13.        #No match
This line contains the number 133.       #No match
This line contains the number 1133.      #Match
This line contains the number 113312.    #Match
This line contains the number 1112.      #No match
This line contains the number 113312312. #Match
This line contains no numbers at all.    #No match

grep 命令如何计算 1133* 正则表达式？

echo "Consider this text file:

TEST FILE : test                         #No match
                                         #No match
Run grep \"1133*\" on this file          #Match
                                         #No match
This line contains the number 113.       #Match
This line contains the number 13.        #No match
This line contains the number 133.       #No match
This line contains the number 1133.      #Match
This line contains the number 113312.    #Match
This line contains the number 1112.      #No match
This line contains the number 113312312. #Match
This line contains no numbers at all.    #No match" | grep "1133*"

输出:

Run grep "1133*" on this file            #Match
This line contains the number 113.       #Match
This line contains the number 1133.      #Match
This line contains the number 113312.    #Match
This line contains the number 113312312. #Match

为什么包含 113 的行是正数？

正则表达式 1133* 是否意味着除了找到包含单词 1133+anything else 的所有行？

这个例子是在 tldp regexp 上找到的文档页面。

Answer 1

您正在考虑一个 shell 通配符，其中 * 匹配任何内容。在 regular expressions , * 是 quantifier这意味着它之前的任何内容的“零个或多个”，在本例中为 3。

因此您的表达式表示 113 后跟零个或多个 3。