Ruby Regex匹配意外字符

Question

I am trying to write a script that parses filename of a comicbook and tries to extract info such as Seriesname, Publication year etc.In this case, I am trying to extract publication year from the name. Consider the following name, I would need to match and get value 2003. Below is the expression I had for this.

r = %r{ (?i)(^|[,\s-_])v(\d{4})($|[,\s-_]) }

However this matches the number irrespective of what character I have before the v or after the number

I expect the first two to not match and the third to match.

• 010 - All Star Batman & Robin The Boy Wonder 01 - av2003
• 010 - All Star Batman & Robin The Boy Wonder 01 - v2003t
• 010 - All Star Batman & Robin The Boy Wonder 01 - v2003

What am I doing wrong in this case?

Answer 1

Inside character classes (ie. [] s) the - character has a special meaning when it's between two other characters: it creates a range starting the character before and ending at the character after.

Here, you want it literally, so you should either escape the - or (more idiomatically in regex) put it as the first or last character in the [] .

Also, btw, you have literal space characters, but no /x modifier, also you probably don't want to capture what's before and after the year, so the final pattern would be:

%r{(?i)(?:^|[,\s_-])v(\d{4})(?:$|[,\s_-])}

Answer 2

@smathy answered your question (rather nicely). I want to point out that you could write your regex without a capture group:

 r = /
     (?:         # begin a non-capture group 
       ^|[,\s_-] # match the beginning of the string, a ws char or char in ',_-'
     )           # end the non-capture group
     v           # match v
     \K          # forget everything matched so far
     \d{4}       # match 4 digits
     (?=         # begin a positive look-ahead
       $|[,\s_-] # match the end of the string, a ws char or char in ',_-'
     )           # end positive lookahead
     /x

"010 - All Star Batman & Robin The Boy Wonder 01 - av2003"[r]
  #=> nil 
"010 - All Star Batman & Robin The Boy Wonder 01 - v2003t"[r]
  #=> nil 
"010 - All Star Batman & Robin The Boy Wonder 01 - v2003"[r]
  #=> "2003

• If you wish to match v or V , change the line v to [vV] .
• If you wish the regex to be case independent, change /x to /ix (in which case there is no need to replace v with [vV] ).
• If you wish to ensure the publication date is (say) in the 20th or 21st century, change \\d{4} to [12]\\d{3} .
• You could alternatively change the non-capture group to a positive lookbehind ( (?<=^|[,\\s_-]) ) and delete \\K .