Help with pattern matching


 
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# 1  
Old 03-14-2010
Help with pattern matching

I have a group of strings like:

Code:
[[something and something [[like this]] and this [[but]] here is [[what]].]] [[another big string [[with other]] substrings.]]

I need a regular expression/way to extract those strings like so:

Code:
string1 => something and something [[like this]] and this [[but]] here is [[what]].
string2 => another big string [[with other]] substrings.

I tried (PHP):
preg_match("/\[\[(.+?)\]\]/"...
but this obviously catches: something and something [[like this

I was looking for something simple and more elegant but of course I can solve the problem going from char to char and counting the number of open/close brackets to identify when they are really closed...

You can answer in any language...
# 2  
Old 03-14-2010
For the SPECIFIC example you posted, this works.

Code:
$ echo "[[something and something [[like this]] and this [[but]] here is [[what]].]] [[another big string [[with other]] substrings.]]" \
| perl -nle 'print "$1\n$2" if (/\[\[(.*\]\]\.)\]\]\s+(\[\[.*\.)\]\]/);'
something and something [[like this]] and this [[but]] here is [[what]].
[[another big string [[with other]] substrings.
$

Are the "[[" the delimiters of something? Are the ".]]" the break to a new string? If so, there may be an easier regex combined with global matches or a loop.

I cannot recommend more highly using an interactive regex tool. What seems hard is really easy when you see it working realtime.

I use RegExr: Online Regular Expression Testing Tool but there are others, including ones that duplicate the specific regex flavor you are using.

Last edited by drewk; 03-14-2010 at 05:21 PM.. Reason: typo...
# 3  
Old 03-15-2010
Quote:
Originally Posted by drewk
For the SPECIFIC example you posted, this works.

Code:
$ echo "[[something and something [[like this]] and this [[but]] here is [[what]].]] [[another big string [[with other]] substrings.]]" \
| perl -nle 'print "$1\n$2" if (/\[\[(.*\]\]\.)\]\]\s+(\[\[.*\.)\]\]/);'
something and something [[like this]] and this [[but]] here is [[what]].
[[another big string [[with other]] substrings.
$

Are the "[[" the delimiters of something? Are the ".]]" the break to a new string? If so, there may be an easier regex combined with global matches or a loop.

I cannot recommend more highly using an interactive regex tool. What seems hard is really easy when you see it working realtime.

I use RegExr: Online Regular Expression Testing Tool but there are others, including ones that duplicate the specific regex flavor you are using.
Yes, that works, but the problem is that the strings change in size and in number of substrings, and the .]] also may change!

Another example:
Code:
[[something is something]] [[and then I was [[wondering]] why is  [[this like so]]]] [[anyway I think [[that]] I [[can]] go to]]]] [[blabla]] [[bla bla [[foo]] [[bar]]]] [[foobar]] [[not]]

The [[ ]] are the delimiters of the string, however that string can have substrings ALSO delimited by [[ ]]

Thanks for your reply...
# 4  
Old 03-15-2010
Code:
[[something is something]] [[and then I was [[wondering]] why is  [[this like so]]]]

If you were ever unfortunate and had to code lisp, this was a common problem.
There was a kind of descent parse: incrementing and decrementing a counter. When the counter got back to zero you were at the end of the line/command.

C:
Code:
int foo(char *src)
{
   char dest[80][120]={0x0};
   char *p=NULL;
   char *q=NULL;
   int line=0;
   int count=0;

   for(p=src, q=dest[line]; *p; p++)
   {
        if(*p=='[') count++;
        if(*p==']') count--;
        if(!count && *p==']')
        {
              line++;
              q=dest[line];
             
        }
        if(!count) continue;
        *q=*p;
          q++;
   }
}

You will have to knock off the leading and trailing square brackets. This also does not handle inter-string characters like spaces.

Last edited by jim mcnamara; 03-15-2010 at 11:54 AM..
# 5  
Old 03-15-2010
Quote:
Originally Posted by redoubtable
Yes, that works, but the problem is that the strings change in size and in number of substrings, and the .]] also may change!

Another example:
Code:
[[something is something]] [[and then I was [[wondering]] why is  [[this like so]]]] [[anyway I think [[that]] I [[can]] go to]]]] [[blabla]] [[bla bla [[foo]] [[bar]]]] [[foobar]] [[not]]

The [[ ]] are the delimiters of the string, however that string can have substrings ALSO delimited by [[ ]]

Thanks for your reply...
So what specifically is the delimiter and the action desired?

In your first example, the "[[sub strings]]" were kept in the broken out string 1 and string 2. Are all the enclosing [[ and ]] ultimately enclosing separate strings that will be recursively knocked down? In your example, you only showed one break on the ".]]"
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