ruby正则表带式对象使用备忘

ruby对于正则表达式的使用是非常灵活的,提供了专门的正则表达式对象Regexp.其包括match实例方法,字符串也含有该方法.so可以这么做:

/a/ =~ "a"
"a" =~ /a/
"a".match("a")
/a/.match("a")

但是在新版的ruby中不可以这样:

"a" =~ "a" #error!

另外正则的比较还可以用操作符===,其返回true/false表示是否匹配,但是对调一下结果就不一样,这点要注意:

irb(main):079:0> "a"===/a/
=> false
irb(main):080:0> /a/==="a"
=> true

下面举一个例子:

irb(main):083:0> str
=> "vax12345tn19980202.!!!"
irb(main):084:0> v = str.match(/a(.)(\d+)(\D{1,5})(\d+)([,.:]?)/)
=> #<MatchData "ax12345tn19980202." 1:"x" 2:"12345" 3:"tn" 4:"19980202" 5:".">
irb(main):085:0> v[0]
=> "ax12345tn19980202."
irb(main):086:0> v[1]
=> "x"
irb(main):087:0> v[3]
=> "tn"
irb(main):088:0> v.begin 0
=> 1
irb(main):089:0> v.begin 3
=> 8
irb(main):090:0> v.end 3
=> 10
irb(main):091:0> v.offset 3
=> [8, 10]
irb(main):092:0> v.post_match
=> "!!!"
irb(main):093:0> v.pre_match
=> "v"
irb(main):094:0> v.string
=> "vax12345tn19980202.!!!"
irb(main):095:0> v[2]
=> "12345"

为了使用方便(类似于用过就丢代码),也有全局匹配的正则表达式对象$~,操作和上面类似:

irb(main):097:0> str.match(/a(.)(\d+)(\D{1,5})(\d+)([,.:]?)/)
=> #<MatchData "ax12345tn19980202." 1:"x" 2:"12345" 3:"tn" 4:"19980202" 5:".">
irb(main):098:0> $~
=> #<MatchData "ax12345tn19980202." 1:"x" 2:"12345" 3:"tn" 4:"19980202" 5:".">
irb(main):099:0> $&
=> "ax12345tn19980202."
irb(main):100:0> $`
=> "v"
irb(main):101:0> $'
=> "!!!"
irb(main):102:0> $+
=> "."
irb(main):103:0> $1
=> "x"
irb(main):104:0> $2
=> "12345"
irb(main):105:0> $3
=> "tn"

对于字符串也含有一些正则的表达式的实例方法,比如sub,gsub,scan等等,其中在sub,gsub之类的方法中第二个参数可以使用置换变量来表示:\&和\0表示整个匹配的字符串,\1至\9是第n个括号内匹配的字符串,另外也可以用\`,\'和\+它们和$`,$'和$+相对应:

irb(main):117:0> s="abc12345xyz"
=> "abc12345xyz"
irb(main):118:0> s.sub(/(\d+)/,'(\&)')
=> "abc(12345)xyz"