From: Robert Klemme <shortcutter@...>
Date: 2009-01-13T04:39:18+09:00
Subject: Re: Does ruby support global expression?

On 12.01.2009 15:33, Robert Dober wrote:
> On Mon, Jan 12, 2009 at 2:59 PM, Jarod Zhu <zhujie2003info@gmail.com> wrote:
>> Hi, all
>>
>>     In my project, there are some rules using global expression( '*'
>> as one or more characters ) to match some functions' output.
>>     Such as:
>>     rule1：  the * apple   (will match the output "the red apple")
>>     rule2：  the * + * game    (will match the output "the wonderful +
>> successful game")
>>
>>     I want to use ruby to realize the match check, but I only know
>> ruby supports regular expression.
>> So I have to change rules to the form of regular expressions( "*" => ".
>> +" and add '\' to other regular expession keywords like '+', '.' etc.)
>>
>>     Is there any way to use global expression directly in ruby?
> No, better make it ourselves
> 
> class String
>   def escape
>     return "" if empty?
>     Regexp::escape self
>   end
>   def glob? a_string
>     Regexp::new(
>       scan( /(.*?)\*([^*]*)/ ).
>         inject("") { | r , ( prefix, suffix ) | r << prefix.escape <<
> '\w+' << suffix.escape }
>     ).match( a_string )
>   end
> end
> 
> p "ab *c*d*".glob?( "ab andcordequally" )
> p "a*b".glob?( "ab" )
> p "etc.etc."

Small remark: I'd split this up, i.e.

class String
   def to_glob
     Regexp::new(
       scan( /(.*?)\*([^*]*)/ ).
         inject("") { | r , ( prefix, suffix ) |
           r << prefix.escape << '\w+' << suffix.escape }
     )
   end
end

This makes for more efficient matching if the pattern is to be applied 
to multiple strings.

Here's how I'd do it:

class String
   def to_glob
     Regexp.new('\\A' << gsub(/\\([^*?])/, '\\1').split(/(\\?[*?])/).map 
do |s|
       case s
       when '*': '.*'
       when '?': '.'
       when '\\*', '\\?': s
       else Regexp.escape(s)
       end
     end.join << '\\z')
   end
end

gl = "foo*b\\ar\\*a".to_glob
p gl

%w{foo foobar*a foo123bar foobar*a}.each do |s|
   p [s, gl =~ s]
end

Kind regards

	robert


-- 
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