笔记一
笔记源自 RegexOne
需要转义的特殊字符：
* . ? + $ ^ [ ] ( ) { } | \ /
\s匹配所有空格字符，等同于： [\t\n\f\r\p{Z}]\f换页符\n换行符\r回车符\t制表符\p等同于\r\n, CRLF DOS 行终止符
Tutorials
Lesson 1 The 123s
\d any single digit character
\D any single non-digit character
Lesson 2: The Dot
. any single character
\. period
Lesson 3: Matching specific characters
[abc] only a, b, c single character
Lesson 4: Excluding specific characters
[^abc] not a, b or c
Lesson 5: Character ranges
[a-z] characters a to z
[0-9] number 0 to 9
\w 字母，数字，下划线。等价于[A-Za-z0-9_]
\W 等价于\[^A-Za-z0-9_]
Lesson 6: Catching some zzz’s
{m} m repetitions
{m, n} m to n repetitions
Examples:
w{3} (three w)
[wxy]{5} (five characters, each of which can be a w, x, or y)
Lesson 7: Mr. Kleene, Mr. Kleene
* zero or more repetitions *前的字符可以重复 0 次或者更多次
+ one or more repetitions +前的字符可以重复 1 次或者更多次
Match aaaabcc
Match aabbbbc
Match aacc
Skip a
answer: aa+b*c+
Lesson 8: Characters optional
? optional character ?前的字符可以出现 0 次或者 1 次
ab?c will match either the strings “abc” or “ac”
Lesson 9: All this whitespace
\s 代替 any whitespace 包括 space, tab(\t), new line(\n), return(\r)
\S 相反
Lesson 10: Starting and ending
^...$ starts and ends
^Mission: successful$ 文本必须以 Mission: 开头，successful 结尾
Lesson 11: Match groups
捕获组：
(...)：匹配字符并创建捕获组
(a(bc)) capture sub-group
(.*) capture all
非捕获组：
(?:...): 匹配字符但不创建捕获组
Lesson 14: It’s all conditional
(abc|def) matches abc or def
笔记二
下面的笔记源自 github 正则表达式教程
4. 零宽度断言
正先行断言 (positive lookahead)：(?=...)，匹配位置的后面有指定模式
负先行断言 (negative lookahead)：(?!...)，匹配位置的后面没有指定模式
正后发断言 (positive lookbehind)：(?<=...) 匹配位置的前面有指定模式
负后发断言 (negative lookbehind)：(?<!...) 匹配位置的前面没有指定模式
比如对于字符串 foobarbarfoo
bar(?=bar) finds the 1st bar ("bar" which has "bar" after it)
bar(?!bar) finds the 2nd bar ("bar" which does not have "bar" after it)
(?<=foo)bar finds the 1st bar ("bar" which has "foo" before it)
(?<!foo)bar finds the 2nd bar ("bar" which does not have "foo" before it)
(?<=foo)bar(?=bar) finds the 1st bar ("bar" with "foo" before it and "bar" after it)
5. 标志
/pattern/flags, 其中 flags 有：
- i 忽略大小写。
- g 全局搜索，返回全部匹配。
- m 多行修饰符：锚点元字符 ^ $ 工作范围在每行的起始。
6. 贪婪匹配和惰性匹配
默认是贪婪匹配，使用?转化为惰性匹配。
"/(.*at)/" => The fat cat sat on the mat.
"/(.*?at)/" => The fat cat sat on the mat.