Question

What would a regular expression be to find sets of 2 unescaped double quotes that are contained in columns set off by double quotes in a CSV file?

Not a match:

"asdf","asdf"
"", "asdf"
"asdf", ""
"adsf", "", "asdf"

Match:

"asdf""asdf", "asdf"
"asdf", """asdf"""
"asdf", """"

Answer 1

Try this:

(?m)""(?![ \t]*(,|$))

Explanation:

(?m)       // enable multi-line matching (^ will act as the start of the line and $ will act as the end of the line (i))
""         // match two successive double quotes
(?!        // start negative look ahead
  [ \t]*   //   zero or more spaces or tabs
  (        //   open group 1
    ,      //     match a comma 
    |      //     OR
    $      //     the end of the line or string
  )        //   close group 1
)          // stop negative look ahead

So, in plain English: “match two successive double quotes, only if they DON’T have a comma or end-of-the-line ahead of them with optionally spaces and tabs in between”.

(i) besides being the normal start-of-the-string and end-of-the-string meta characters.