C# string.replace to remove illegal characters [duplicate]

System.IO.Path.GetInvalidFileNameChars() has all the invalid characters.

Here's a sample method:

public static string SanitizeFileName
(
  string fileName, 
  char replacementChar = '_'
)
{
  HashSet<char> blocked = new(System.IO.Path.GetInvalidFileNameChars());
  char[] output = fileName.ToCharArray();
  for (int i = 0, ln = output.Length; i < ln; i++)
  {
    if (blocked.Contains(output[i]))
    {
      output[i] = replacementChar;
    }
  }
  return new String(output);
}

As pointed out by pixel, this would translate

my\\\file\\\\\\\\\\name

into

my___file__________name

... which may be unattractive.

If this function is something you might call in a batch or if you'd like the flexibility to replace consecutive invalid characters with a single replacement, you may want something like this:

public class FileNameSanitizer
{
  // cache the blocked characters
  private HashSet<char> _blocked = new(System.IO.Path.GetInvalidFileNameChars());

  /// <summary>Replace individual invalid characters one-for-one.</summary>
  public string Sanitize
  (
    string fileName,
    char replacementChar = '_'
  )
  {    
    char[] output = fileName.ToCharArray();
    for (int i = 0, ln = output.Length; i < ln; i++)
    {
      if (_blocked.Contains(output[i]))
      {
        output[i] = replacementChar;
      }
    }
    return new String(output);
  }
  
  /// <summary>Replace consecutive invalid characters with a single replacement character.</summary>
  public string SanitizeCondensed
  (
    string fileName,
    char replacementChar = '_'
  )
  {
    char[] output = fileName.ToCharArray();
    char current;
    bool replaced = false;
    int i = 0, x = 0, ln = output.Length;
    for (; i < ln; i++)
    {
      current = output[i];
      if (_blocked.Contains(current))
      {
        if (!replaced)
        {
          output[x++] = replacementChar;
        }
        replaced = true;
      }
      else
      {
        output[x++] = current;
        replaced = false;
      }
    }
    return new String(output, 0, x);
  }
}

string charsToRemove = @"\/:";TODO complete this list

string filename;

string pattern = string.format("[{0}]", Regex.Escape(charsToRemove));
Regex.Replace(filename, pattern, "");

If you just want to remove illegal chars, rather than replacing them with something else you can use this.

Have a look at Regex.Replace here, it will do everything you desire when it comes to stripping out characters individually. Selective replacement of other strings may be trickier.