Analyze large CSV file and print max size of each column

Program.cs

// Assumes there is a header line in first row of file
// Usage: dotnet run <input-csv-file>
// Output is table of column names and the maximum size of that column
// On Macbook Pro, 56 million rows of a 32 column CSV takes approximately 2.5 minutes
using System.Text.RegularExpressions;
using System.Text;

namespace CsvUtility
{
    class Program
    {
        // Usage: dotnet run <input csv file>
        // Examines file and prints out the max size of each column
        static void Main(string[] args)
        {
            // get file name argument
            string fileName = args[0];
            // open file
            StreamReader file = new StreamReader(fileName);

            var headerLine = file.ReadLine();
            var header = headerLine?.Split(',');
            if (header == null)
            {
                Console.WriteLine("No header found");
                return;
            }
            var colWidths = new int[header.Length];
            var rowCount = 0;

            while (!file.EndOfStream)
            {
                var line = file.ReadLine();
                if (line != null) {
                    rowCount++;

                    var values = MySplitCSV(line);

                    var fldCtr = 0;
                    foreach (string value in values)
                    {
                        if (value.Length > colWidths[fldCtr])
                        {
                            colWidths[fldCtr] = value.Length;
                        }
                        fldCtr++;
                    }

                    //print every 100000 rows
                    if (rowCount % 100000 == 0)
                    {
                        Console.Write(String.Format("\rProcessed {0:#,0} rows ", rowCount));
                    }
                }
            }

            file.Close();
            Console.WriteLine("\n\nIndex       Column Name                                    Width");
            Console.WriteLine("------------|----------------------------------------------|-------");
            for (var i = 0; i < colWidths.Length; i++)
            {
                Console.WriteLine("{0,10}   {1,-48}{2,6}", i, header[i], colWidths[i]);
            }
            Console.WriteLine("\nTotal rows: " + rowCount);
        }

        static Regex csvSplit = new Regex("(?:^|,)(\"(?:[^\"]+|\"\")*\"|[^,]*)", RegexOptions.Compiled);

        public static string[] SplitCSV(string input)
        {

            List<string> list = new List<string>();
            foreach (Match match in csvSplit.Matches(input))
            {
                var curr = match.Value;
                if (0 == curr.Length)
                {
                    list.Add("");
                }

                list.Add(curr.TrimStart(','));
            }

            return list.ToArray();
        }

        // Regex is slow in SplitCSV() so we use this instead
        public static string[] MySplitCSV(string input)
        {
            bool quote = false;
            StringBuilder sb = new StringBuilder();
            foreach(char c in input)
            {
                if (c == '\"') {
                    quote = !quote;
                }
                if (c == ',' && !quote) {
                    sb.Append('\x01');
                } else {
                    sb.Append(c);
                }
            }
            var result = sb.ToString().Split('\x01');

            return result;
        }
    }
}

Quote handling:

This was written so quoted columns are considered, and that there could be commas inside the quotes (which are ignored).

So, a file containing:

100001,"Kirk, James",Captain

Will process correctly as three columns.