String Replace ignoring case

Question

I have a string called  hello world   I need to replace the word  world  to  csharp   for this I use   string Replace  World    csharp      but as a result  I don t get the string replaced  The reason is case sensitiveness  The original string contains  world  whereas I m trying to replace  World    Is there any way to avoid this case sensitiveness in string Replace method

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below is the alternative to replace string ignoring character case  String thisString    hello world    String replaceString    World      thisString Replace  World    csharp       below is the alternative to replace string ignoring character case  int start   StringUtils indexOfIgnoreCase thisString replaceString   String searchKey   thisString substring start  start replaceString length     thisString  thisString replaceAll searchKey  replaceString    System out println thisString      prints hello World

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Extending Petrucio s answer with Regex Escape on the search string  and escaping matched group as suggested in Steve B s answer  and some minor changes to my taste    public static class StringExtensions       public static string ReplaceIgnoreCase this string str  string from  string to                return Regex Replace str  Regex Escape from   to Replace             RegexOptions IgnoreCase             Which will produce the following expected results   Console WriteLine   heLLo  wOrld  ReplaceIgnoreCase   hello  world    Hi  1 Universe        Hi  1 Universe Console WriteLine  heLLo wOrld  ReplaceIgnoreCase   hello  world    Hi  1 Universe          heLLo wOrld   However without performing the escapes you would get the following  which is not an expected behaviour from a String Replace that is just case-insensitive   Console WriteLine   heLLo  wOrld  ReplaceIgnoreCase NoEscaping   hello  world    Hi  1 Universe         heLLo  wOrld Console WriteLine  heLLo wOrld  ReplaceIgnoreCase NoEscaping   hello  world    Hi  1 Universe          Hi heLLo Universe

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2 5X FASTER and MOST EFFECTIVE method than other s regular expressions methods        lt summary gt      Returns a new string in which all occurrences of a specified string in the current instance are replaced with another      specified string according the type of search to use for the specified string       lt  summary gt       lt param name  str  gt The string performing the replace method  lt  param gt       lt param name  oldValue  gt The string to be replaced  lt  param gt       lt param name  newValue  gt The string replace all occurrences of  lt paramref name  oldValue   gt        If value is equal to  lt c gt null lt  c gt   than all occurrences of  lt paramref name  oldValue   gt  will be removed from the  lt paramref name  str   gt   lt  param gt       lt param name  comparisonType  gt One of the enumeration values that specifies the rules for the search  lt  param gt       lt returns gt A string that is equivalent to the current string except that all instances of  lt paramref name  oldValue   gt  are replaced with  lt paramref name  newValue   gt        If  lt paramref name  oldValue   gt  is not found in the current instance  the method returns the current instance unchanged  lt  returns gt   DebuggerStepThrough  public static string Replace this string str      string oldValue  string  newValue      StringComparison comparisonType            Check inputs      if  str    null                   Same as original  NET C  string Replace behavior          throw new ArgumentNullException nameof str              if  str Length    0                   Same as original  NET C  string Replace behavior          return str            if  oldValue    null                   Same as original  NET C  string Replace behavior          throw new ArgumentNullException nameof oldValue              if  oldValue Length    0                   Same as original  NET C  string Replace behavior          throw new ArgumentException  String cannot be of zero length                   if  oldValue Equals newValue  comparisonType                 This condition has no sense       It will prevent method from replacesing   Example    ExAmPlE    EXAMPLE  to  example        return str                    Prepare string builder for storing the processed string         Note  StringBuilder has a better performance than String by 30-40       StringBuilder resultStringBuilder   new StringBuilder str Length             Analyze the replacement  replace or remove      bool isReplacementNullOrEmpty   string IsNullOrEmpty  newValue             Replace all values      const int valueNotFound   -1      int foundAt      int startSearchFromIndex   0      while   foundAt   str IndexOf oldValue  startSearchFromIndex  comparisonType      valueNotFound                    Append all characters until the found replacement          int  charsUntilReplacment   foundAt - startSearchFromIndex          bool isNothingToAppend    charsUntilReplacment    0          if   isNothingToAppend                        resultStringBuilder Append str  startSearchFromIndex   charsUntilReplacment                           Process the replacement          if   isReplacementNullOrEmpty                        resultStringBuilder Append  newValue                          Prepare start index for the next search             This needed to prevent infinite loop  otherwise method always start search             from the start of the string  For example  if an oldValue     EXAMPLE   newValue     example             and comparisonType     any ignore case  will conquer to replacing              EXAMPLE  to  example  to  example  to  example      infinite loop          startSearchFromIndex   foundAt   oldValue Length          if  startSearchFromIndex    str Length                           It is end of the input string  no more space for the next search                 The input string ends with a value that has already been replaced                  Therefore  the string builder with the result is complete and no further action is required              return resultStringBuilder ToString                             Append the last part to the result      int  charsUntilStringEnd   str Length - startSearchFromIndex      resultStringBuilder Append str  startSearchFromIndex   charsUntilStringEnd         return resultStringBuilder ToString         Note  ignore case    StringComparison OrdinalIgnoreCase as parameter for StringComparison comparisonType  It is the fastest  case-insensitive way to replace all values     Advantages of this method    High CPU and MEMORY efficiency  It is the fastest solution  2 5 times faster than other s methods with regular expressions  proof in the end   Suitable for removing parts from the input string  set newValue to null   optimized for this  Same as original  NET C  string Replace behavior  same exceptions  Well commented  easy to understand  Simpler     no regular expressions  Regular expressions are always slower  because of their versatility  even compiled   This method is well tested and there are no hidden flaws like infinite loop in other s solutions  even highly rated        AsValeO  Not works with Regex language elements  so it s not   universal method       Mike Stillion  There is a problem with this code  If the text in new   is a superset of the text in old  this can produce an endless loop      Benchmark-proof  this solution is 2 59X times faster than regex from  Steve B   code      Results     1 2  Regular expression solution  4486 milliseconds    2 2  Current solution  1727 milliseconds     2 59X times FASTER  than regex      Notes  the test was started 5 times  the result is an average  release build   const int benchmarkIterations   1000000  const string sourceString    aaaaddsdsdsdsdsd   const string oldValue    D   const string newValue    Fod   long totalLenght   0   Stopwatch regexStopwatch   Stopwatch StartNew    string tempString1  for  int i   0  i  lt  benchmarkIterations  i          tempString1   sourceString      tempString1   ReplaceCaseInsensitive tempString1  oldValue  newValue        totalLenght   totalLenght   tempString1 Length    regexStopwatch Stop       Stopwatch currentSolutionStopwatch   Stopwatch StartNew    string tempString2  for  int i   0  i  lt  benchmarkIterations  i          tempString2   sourceString      tempString2   tempString2 Replace oldValue  newValue          StringComparison OrdinalIgnoreCase        totalLenght   totalLenght   tempString2 Length    currentSolutionStopwatch Stop        Original idea      Darky711  thanks  MinerR for StringBuilder

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Net Core has this method built-in  Replace String  String  StringComparison  Doc  Now we can simply write   quot     quot  Replace  quot oldValue quot    quot newValue quot   StringComparison OrdinalIgnoreCase

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You could use a Regex and perform a case insensitive replace   class Program       static void Main                 string input    hello WoRlD           string result               Regex Replace input   world    csharp   RegexOptions IgnoreCase           Console WriteLine result      prints  hello csharp

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You can also try the Regex class   var regex   new Regex   camel   RegexOptions IgnoreCase    var newSentence   regex Replace  sentence   horse

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Use this  Tested and 100  Worked  For VB NET Dim myString As String Dim oldValue As String Dim newValue As String  myString   Form1 TextBox1 Text oldValue   TextBox1 Text newValue   TextBox2 Text  Dim working As String   myString Dim index As Integer   working IndexOf oldValue  StringComparison CurrentCultureIgnoreCase   While index  lt  gt  -1     working   working Remove index  oldValue Length      working   working Insert index  newValue      index   index   newValue Length     index   working IndexOf oldValue  index  StringComparison CurrentCultureIgnoreCase      Form1 TextBox1 Text   working End While  For C  private void Button2 Click System Object sender  System EventArgs e        string myString      string oldValue      string newValue       myString   Form1 TextBox1 Text      oldValue   TextBox1 Text      newValue   TextBox2 Text       string working   myString      int index   working IndexOf oldValue  StringComparison CurrentCultureIgnoreCase        while  index    -1                working   working Remove index  oldValue Length           working   working Insert index  newValue           index   index   newValue Length          index   working IndexOf oldValue  index  StringComparison CurrentCultureIgnoreCase           Form1 TextBox1 Text   working

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Modified  Darky711 s answer to use the passed in comparison type and match the framework replace naming and xml comments as closely as possible        lt summary gt      Returns a new string in which all occurrences of a specified string in the current instance are replaced with another specified string       lt  summary gt       lt param name  str  gt The string performing the replace method  lt  param gt       lt param name  oldValue  gt The string to be replaced  lt  param gt       lt param name  newValue  gt The string replace all occurrances of oldValue  lt  param gt       lt param name  comparisonType  gt Type of the comparison  lt  param gt       lt returns gt  lt  returns gt  public static string Replace this string str  string oldValue  string  newValue  StringComparison comparisonType         newValue    newValue    string Empty      if  string IsNullOrEmpty str     string IsNullOrEmpty oldValue     oldValue Equals  newValue  comparisonType                 return str            int foundAt      while   foundAt   str IndexOf oldValue  0  comparisonType      -1                str   str Remove foundAt  oldValue Length  Insert foundAt   newValue             return str

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Below function is to remove all match word like  this  from the string set  By Ravikant Sonare   private static void myfun         string mystring    thiTHISThiss This THIS THis tThishiThiss  Box       var regex   new Regex  this   RegexOptions IgnoreCase       mystring   regex Replace mystring           string   str   mystring Split           for  int i   0  i  lt  str Length  i                  if  regex IsMatch str i  ToString                           mystring   mystring Replace str i  ToString    string Empty                        Console WriteLine mystring

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Edited  wasn t aware of the  naked link  problem  sorry about that   Taken from here   string myString    find Me and replace ME   string strReplace    me   myString   Regex Replace myString   me   strReplace  RegexOptions IgnoreCase     Seems you are not the first to complain of the lack of case insensitive string Replace

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You can use the Microsoft VisualBasic namespace to find this helper function   Replace sourceString   replacethis    withthis       CompareMethod Text

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I have wrote extension method   public static string ReplaceIgnoreCase this string source  string oldVale  string newVale                if  source IsNullOrEmpty      oldVale IsNullOrEmpty                return source           var stringBuilder   new StringBuilder            string result   source           int index   result IndexOf oldVale  StringComparison InvariantCultureIgnoreCase            while  index  gt   0                        if  index  gt  0                  stringBuilder Append result Substring 0  index                 if  newVale IsNullOrEmpty   IsNot                    stringBuilder Append newVale                stringBuilder Append result Substring index   oldVale Length                 result   stringBuilder ToString                 index   result IndexOf oldVale  StringComparison InvariantCultureIgnoreCase                      return result          I use two additional extension methods for previous extension method       public static bool IsNullOrEmpty this string value                return string IsNullOrEmpty value              public static bool IsNot this bool val                return val    false

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Lots of suggestions using Regex  How about this extension method without it   public static string Replace this string str  string old  string  new  StringComparison comparison         new    new            if  string IsNullOrEmpty str     string IsNullOrEmpty old     old Equals  new  comparison           return str      int foundAt   0      while   foundAt   str IndexOf old  foundAt  comparison      -1                str   str Remove foundAt  old Length  Insert foundAt   new           foundAt     new Length            return str

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Doesn t this work  I cant imaging anything else being much quicker or easier   public static class ExtensionMethodsString       public static string Replace this String thisString  string oldValue  string newValue  StringComparison stringComparison                string working   thisString          int index   working IndexOf oldValue  stringComparison           while  index    -1                        working   working Remove index  oldValue Length               working   working Insert index  newValue               index   index   newValue Length              index   working IndexOf oldValue  index  stringComparison                     return working

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I prefer this -  Hello World  ToLower   Replace   world    csharp

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Extensions make our lives easier   static public class StringExtensions       static public string ReplaceInsensitive this string str  string from  string to                str   Regex Replace str  from  to  RegexOptions IgnoreCase           return str

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var search    world   var replacement    csharp   string result   Regex Replace      stringToLookInto      Regex Escape search        replacement Replace                 RegexOptions IgnoreCase      The Regex Escape is useful if you rely on user input which can contains Regex language elements  Update  Thanks to comments  you actually don t have to escape the replacement string   Here is a small fiddle that tests the code    using System  using System Text RegularExpressions             public class Program       public static void Main                  var tests   new                 new   Input  abcdef   Search  abc   Replacement  xyz   Expected  xyzdef                 new   Input  ABCdef   Search  abc   Replacement  xyz   Expected  xyzdef                 new   Input  A BCdef   Search  a bc   Replacement  xyz   Expected  xyzdef                 new   Input  abcdef   Search  abc   Replacement  x yz   Expected  x yzdef                        new   Input  abcdef   Search  abc   Replacement      Expected   def                          foreach var test in tests               var result   ReplaceCaseInsensitive test Input  test Search  test Replacement                Console WriteLine                   Success   0   Actual   1    2                    result    test Expected                  result                  test                                        private static string ReplaceCaseInsensitive string input  string search  string replacement           string result   Regex Replace              input              Regex Escape search                replacement Replace                         RegexOptions IgnoreCase                    return result            Its output is   Success  True  Actual  xyzdef    Input   abcdef  Search   abc  Replacement   xyz  Expected   xyzdef    Success  True  Actual  xyzdef    Input   ABCdef  Search   abc  Replacement   xyz  Expected   xyzdef   Success  True  Actual  xyzdef    Input   A BCdef  Search   a bc  Replacement   xyz  Expected   xyzdef    Success  True  Actual  x yzdef    Input   abcdef  Search   abc  Replacement   x yz  Expected   x yzdef   Success  True  Actual   def    Input   abcdef  Search   abc  Replacement      Expected    def

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Using  Georgy Batalov solution I had a problem when using the following example  string original    blah DC bleh DC blih DC bloh DC com   string replaced   original ReplaceIgnoreCase   DC          Below is how I rewrote his extension  public static string ReplaceIgnoreCase this string source  string oldVale   string newVale                if  source IsNullOrEmpty      oldVale IsNullOrEmpty                return source           var stringBuilder   new StringBuilder            string result   source           int index   result IndexOf oldVale  StringComparison InvariantCultureIgnoreCase           bool initialRun   true           while  index  gt   0                        string substr   result Substring 0  index               substr   substr   newVale              result   result Remove 0  index               result   result Remove 0  oldVale Length                stringBuilder Append substr                index   result IndexOf oldVale  StringComparison InvariantCultureIgnoreCase                      if  result Length  gt  0                        stringBuilder Append result                      return stringBuilder ToString

[c#] String.Replace ignoring case

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