How to get substring of comma delimited string?

[astossyadvili]

I have a comma delimited string and want the first 100 entries (not including the 100th comma) as a single string.So for example if I had the string \[code\]a,b,c,d,e,f,g\[/code\]And the problem was get the first 3 entries, the desired result string would be\[code\]a,b,c\[/code\]