Ruby正则表达式在匹配包含\\ n个字符的字符串时返回意外结果

Question

Below is the output from my irb console

2.3.2 :001 > str = "Whenever ThingA happens\nrepeats: Sunday, Monday and Tuesday\n\n\nDo ThingB"
 => "Whenever ThingA happens\nrepeats: Sunday, Monday and Tuesday\n\n\nDo ThingB"

2.3.2 :002 > str.match(/(.*)\s*(?:repeats)/)
 => #<MatchData "Whenever ThingA happens\nrepeats" 1:"Whenever ThingA happens">

2.3.2 :003 > str.match(/(.*)(?:repeats)/)
 => #<MatchData "repeats" 1:"">

Can anybody please help me understand what's going on with the 2nd regex /(.*)(?:repeats)/ which is causing it not return the expected result the 1st regex /(.*)\\s*(?:repeats)/ returns?

On rubular.com 2nd regex shows following match 1. Whenever ThingA happens\\n which is expected however Ruby's String#match returns unexpected results as shown in console output above.

Answer 1

The dot does not match new line characters so it is selecting the character before repeats for the given line, which is nothing. Essentially the same as /(?=repeats)/ since repeats this the first word on this line.

Adding the m flag (make dot match newlines) will solve this for you

str.match(/(.*)repeats/m)
#=> #<MatchData "Whenever ThingA happens\nrepeats" 1:"Whenever ThingA happens\n">

The reason the first one works is becuase \\s indicates a whitespace character and that does match the new line \\n since new line is a whitespace character.

The noncapture group has no impact as pointed out by @CarySwoveland