regular expression should split , that are contained outside the double quotes in a CSV file?

Question

This is the sample

\"abc\",\"abcsds\",\"adbc,ds\",\"abc\"

Output should be

abc
abcsds
adbc,ds
abc

Answer 1

This is a tougher job than you realize -- not only can there be commas inside the quotes, but there can also be quotes inside the quotes. Two consecutive quotes inside of a quoted string does not signal the end of the string. Instead, it signals a quote embedded in the string, so for example:

"x", "y,""z"""

should be parsed as:

x
y,"z"

So, the basic sequence is something like this:

Find the first non-white-space character.
If it was a quote, read up to the next quote. Then read the next character.
    Repeat until that next character is not also a quote.
    If the next (non-whitespace) character is not a comma, input is malformed.
If it was not a quote, read up to the next comma.
Skip the comma, repeat the whole process for the next field.

Note that despite the tag, I'm not providing a regex -- I'm not at all sure I've seen a regex that can really handle this properly.