Ruby 谁给解释一下，后两个正则表达式是什么意思

race · March 10, 2012 · Last by alucardpj replied at March 12, 2012 · 3156 hits

'12345678'.slice(/.*(?=567)/)
# => "1234" 
'12345678'.slice(/(?<=123).*/)
# => "45678" 
'12345678'.slice(/(?!123).*/)
# => "2345678" 
'12345678'.slice(/.*(?<!567)/)
# => "12345678" 
'12345678'.slice(/.*(?<!5678$)/)
# => "1234567"

natsuki #1 March 10, 2012

斷言所匹配的位置後面不是 567，如果是則匹配失敗，具體來說你的.*在某一時刻一定匹配了一些字符的，如果這時候他所匹配的位置後面是 567 則認為匹配失敗，繼續貪婪或者回溯

dreamrise #2 March 11, 2012

求解释 (?= ) 是什么意思？

alucardpj #3 March 12, 2012

http://deerchao.net/tutorials/regex/regex.htm#backreference

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