Thank you Monks for the suggestions. They help but not fully. The problem is as follows: the sentence above itself can assume several forms. The idea is to catch the following pattern in a sentence, here is the pseudo regular expression (space is shown here as ' '): \(? \*.+?\* , \*.+?\* ... \*.+?\* , and \*.+?\* \)?

I tried to match this pattern using something like: { $line=~/\(?\s(\*.+?\*\s(\,\s)?)+and\*.+?\*\s\)?/; } but it does not work.

This pattern in a sentence can potentially appear anaywhere in a sentence, such as, start, middle, or end of sentence. Also, there can be multiple such patterns in a single sentence. For example, the pattern can appear as (a comma may or may not be present before 'and'):

*q(53)* and *s7* are related with: ( *r:72* , *p/93* , and *s8* ) , and they are also related with *s:2* , *u6* , *g78* but not *s8* . In this example I want to cluster and tag, "*q(53)* and *s7*", "*r:72* , *p/93* , and *s8*" and "*s:2* , *u6* , *g78*" together in the sentence such that the sentence will look like:

*q(53)#and#s7* are related with: *(#r:72#,#p/93#,#and#s8#)* , and they are also related with *s:2#,#u6#,#g78* but not *s8* . Please note that when there is 'but not' then only the preceding part of the pattern is selected.

Thanks very much.