Chapter 3. Regular Expressions（正则表达式）

20. Regular Expression Fundamentals（正则表达式基础）

1. Beginning of line (^ )
2. End of line ( $)
3. Single Character (.)
4. Zero or more Occurrences (*)
5. One or more Occurrence (\+)
6. Zero or one Occurrence (\?)
7. Escaping the Special Character (\)
8. Character Class ([0-9])

   21. Additional Regular Expressions （扩展正则表达式）

9. OR Operation (|)
10. Exactly M Occurrences ({m})
11. M to N Occurrences ({m,n})
12. Word Boundary (\b)（单词边界符）
13. Back References (\n)（反向引用，n为数字）

    22. Sed Substitution Using Regular Expression

    Convert the DOS file format to Unix file format using sed:

    使用sed将DOS下的新行换行符(CR/LF)替换成Unix下的格式

    sed 's/.$//' filename