Regex to split a CSV

I know this (or similar) has been asked many times but having tried out numerous possibilities I've not been able to find a a regex that works 100%.

I've got a CSV file and I'm trying to split it into an array, but encountering two problems: quoted commas and empty elements.

The CSV looks like:

123,2.99,AMO024,Title,"Description, more info",,123987564

The regex I've tried to use is:

thisLine.split(/,(?=(?:[^\"]*\"[^\"]*\")*(?![^\"]*\"))/)

The only problem is that in my output array the 5th element comes out as 123987564 and not an empty string.

Solution

Description

Instead of using a split, I think it would be easier to simply execute a match and process all the found matches.

This expression will:

divide your sample text on the comma delimits
will process empty values
will ignore double quoted commas, providing double quotes are not nested
trims the delimiting comma from the returned value
trims surrounding quotes from the returned value
if the string starts with a comma, then the first capture group will return a null value

Regex: (?:^|,)(?=[^"]|(")?)"?((?(1)[^"]*|[^,"]*))"?(?=,|$)

enter image description here

Example

Sample Text

123,2.99,AMO024,Title,"Description, more info",,123987564

ASP example using the non-java expression

Set regEx = New RegExp
regEx.Global = True
regEx.IgnoreCase = True
regEx.MultiLine = True
sourcestring = "your source string"
regEx.Pattern = "(?:^|,)(?=[^""]|("")?)""?((?(1)[^""]*|[^,""]*))""?(?=,|$)"
Set Matches = regEx.Execute(sourcestring)
  For z = 0 to Matches.Count-1
    results = results & "Matches(" & z & ") = " & chr(34) & Server.HTMLEncode(Matches(z)) & chr(34) & chr(13)
    For zz = 0 to Matches(z).SubMatches.Count-1
      results = results & "Matches(" & z & ").SubMatches(" & zz & ") = " & chr(34) & Server.HTMLEncode(Matches(z).SubMatches(zz)) & chr(34) & chr(13)
    next
    results=Left(results,Len(results)-1) & chr(13)
  next
Response.Write "<pre>" & results

Matches using the non-java expression

Group 0 gets the entire substring which includes the comma
Group 1 gets the quote if it's used
Group 2 gets the value not including the comma

[0][0] = 123
[0][1] = 
[0][2] = 123

[1][0] = ,2.99
[1][1] = 
[1][2] = 2.99

[2][0] = ,AMO024
[2][1] = 
[2][2] = AMO024

[3][0] = ,Title
[3][1] = 
[3][2] = Title

[4][0] = ,"Description, more info"
[4][1] = "
[4][2] = Description, more info

[5][0] = ,
[5][1] = 
[5][2] = 

[6][0] = ,123987564
[6][1] = 
[6][2] = 123987564

Edited

As Boris pointed out CSV format will escape a double quote " as a double double quote "". Although this requirement wasn't included by the OP, if your text includes double double quotes then you'll want to use a this modified expression:

Regex: (?:^|,)(?=[^"]|(")?)"?((?(1)(?:[^"]|"")*|[^,"]*))"?(?=,|$)

It should also be pointed out that Regex is a pattern matching tool not a parsing engine. Therefore if your text includes double double quotes it will still contain the double double quotes after pattern matching is completed. With this solution you'd still need to search for the double double quotes and replace them in your captured text.