Ruby小笔记，持续补充

• 逻辑或运算符作用，判断空值的语法糖

a=nil

a||=333  则 a=333

 

• inject的语法糖

inject(initial, sym) → obj inject(sym) → obj inject(initial) {| memo, obj | block } → obj inject {| memo, obj | block } 

例如  (5..10).inject(1,:+) 与 (5..10).inject(1) {|sum,n| sum+n}

•  ruby gem 不下载rdoc ri

vim ~/.gemrc

gem: --no-ri --no-rdoc

 

• ruby的正则表达式

        http://rubular.com/

[abc]	A single character: a, b or c
[^abc]	Any single character but a, b, or c
[a-z]	Any single character in the range a-z
[a-zA-Z]	Any single character in the range a-z or A-Z
^	Start of line
$	End of line
\A	Start of string
\z	End of string

.	Any single character
\s	Any whitespace character
\S	Any non-whitespace character
\d	Any digit
\D	Any non-digit
\w	Any word character (letter, number, underscore)
\W	Any non-word character
\b	Any word boundary character

(...)	Capture everything enclosed
(a|b)	a or b
a?	Zero or one of a
a*	Zero or more of a
a+	One or more of a
a{3}	Exactly 3 of a
a{3,}	3 or more of a
a{3,6}	Between 3 and 6 of a

 

•  类似awk的文本处理，命令行方式

            awk参考 http://www.cnblogs.com/chengmo/archive/2010/10/06/1844818.html 和 man awk

            cat /etc/passwd |awk -F: '/root/{print $1}' 

            或者

            awk -F: '/root/{print $1}' /etc/passwd

            ruby实现

            cat /etc/passwd |grep root |ruby -F: -ane 'puts $F[0]'

            注意要使用$类预定义变量，用双引号的时候，需要使用#{$_}计算变量值 

             cat /etc/passwd |grep root|ruby -ne 'a=$_.match(/\d+/);puts "#{$.} #{a} #{$_}" '

• Rubygem出现“too many connection resets ”错误

          gem install 出现：删除用户目录下的.gem目录，以及gem的各种cache

          push gem 出现：http://help.rubygems.org/discussions/problems/715-too-many-connection-resets

 

• Ruby正则表达式一特殊语法

             a = "hello there"

            a[/[aeiou](.)\1/, 1] #=> "l"

• *的匹配

一般来说*用于把一个array展开： 

      a, *b = [1,2,3]  ＃a = 1, b = [2,3]  

     引用 http://www.iteye.com/topic/24642