Shell Programming and Scripting

I was looking at a library that lets me parse comma delimited csv files without a problem, but unfortunately, I'm not allowed to make use of that library. I understand that the library probably does something similar to a string split(), but I don't quite know what kind of regular expression is being used for something that's within double quotes, but contains a comma while the line is comma delimited. for instance:

a, "b", "a,b,c", d

Should only be 4 columns. What kind of regular expression would indicate this?

Thanks for your answers in advance.

i think you should split on commas, and then iterate over the resulting array
in the loop, check for elements that start with double quote, and concatenate to it all ensuing elements until the one that ends with "
if you know the number of columns in advance, much easier, if not still doable.