How do I replace the *first instance* of a string in .NET?

by 
string ReplaceFirst(string text, string search, string replace)
{
  int pos = text.IndexOf(search);
  if (pos < 0)
  {
    return text;
  }
  return text.Substring(0, pos) + replace + text.Substring(pos + search.Length);
}

Example:

string str = "The brown brown fox jumps over the lazy dog";

str = ReplaceFirst(str, "brown", "quick");

EDIT: As @itsmatt mentioned, there’s also Regex.Replace(String, String, Int32), which can do the same, but is probably more expensive at runtime, since it’s utilizing a full featured parser where my method does one find and three string concatenations.

EDIT2: If this is a common task, you might want to make the method an extension method:

public static class StringExtension
{
  public static string ReplaceFirst(this string text, string search, string replace)
  {
     // ...same as above...
  }
}

Using the above example it’s now possible to write:

str = str.ReplaceFirst("brown", "quick");

More Related Contents:

  1. Find and extract a number from a string
  2. Is there an alternative to string.Replace that is case-insensitive?
  3. Remove text in-between delimiters in a string (using a regex?)
  4. Need to perform Wildcard (*,?, etc) search on a string using Regex
  5. Count regex replaces (C#)
  6. Regex replace multiple groups
  7. Regex : how to get words from a string (C#)
  8. Regex nested parentheses
  9. How to replace the text between two characters in c#
  10. .NET String.Format() to add commas in thousands place for a number
  11. Easiest way to read from and write to files
  12. Easiest way to split a string on newlines in .NET?
  13. Replace “\\” with “\” in a string in C#
  14. Add spaces before Capital Letters
  15. Replace multiple characters in a C# string
  16. Remove HTML tags from string including &nbsp in C#
  17. Compare String and Object in C#
  18. Translate Perl regular expressions to .NET
  19. How does StringBuilder work internally in C#?
  20. Are Java and C# regular expressions compatible?
  21. Truncate string on whole words in .NET C#
  22. C# – Regex for file paths e.g. C:\test\test.exe
  23. What method in the String class returns only the first N characters?
  24. How can I Unescape and Reescape strings in .net?
  25. What does the @ prefix do on string literals in C#
  26. How to sort list of Ip Addresses using c#
  27. Regular expression to find and remove duplicate words
  28. Replace non-numeric with empty string
  29. Parsing formatted string
  30. is there a elegant way to parse a word and add spaces before capital letters

Leave a Comment