VB.NET

Regular Expression Replace Capture Groups

See more Regular Expressions Examples

Demonstrates replacing capture groups for a regular expression.

Note: Chilkat uses PCRE2. See PCRE2 Regular Expressions
Also see: PCRE2 Performance

VB.NET

Dim success As Boolean = False

Dim subject As String = "John Anders, +_+_+ Mary Robins $$$$"
Dim pattern As String = "(?<first>\w+)\s+(?<last>\w+)"

Dim sb As New Chilkat.StringBuilder
sb.Append(subject)

Dim json As New Chilkat.JsonObject
json.EmitCompact = False

Dim timeoutMs As Integer = 2000
Dim numMatches As Integer = sb.RegexMatch(pattern,json,timeoutMs)
If (numMatches < 0) Then
    ' Probably an error in the regular expression.
    ' Suggestion: Use AI to help create and/or diagnose regular expressions.
    Debug.WriteLine(sb.LastErrorText)
    Exit Sub
End If


' Examine the matches:
Debug.WriteLine(json.Emit())

' There are 2 matches:

' {
'   "named": {
'     "first": 1,
'     "last": 2
'   },
'   "match": [
'     {
'       "group": [
'         {
'           "cap": "John Anders",
'           "idx": 0,
'           "len": 11
'         },
'         {
'           "cap": "John",
'           "idx": 0,
'           "len": 4
'         },
'         {
'           "cap": "Anders",
'           "idx": 5,
'           "len": 6
'         }
'       ]
'     },
'     {
'       "group": [
'         {
'           "cap": "Mary Robins",
'           "idx": 19,
'           "len": 11
'         },
'         {
'           "cap": "Mary",
'           "idx": 19,
'           "len": 4
'         },
'         {
'           "cap": "Robins",
'           "idx": 24,
'           "len": 6
'         }
'       ]
'     }
'   ]
' }

' To replace capture groups, write code to examine each capture group within
' each match, and provide a replacement string.
' Then call RegexReplace.

' For example, let's capitalize the first names, and add append "on" to the last name.
' After doing replacements, we should get:  JOHN Anderson, +_+_+ MARY Robinson $$$$

Dim firstNameIdx As Integer = json.IntOf("named.first")
Dim lastNameIdx As Integer = json.IntOf("named.last")

Dim sbTemp As New Chilkat.StringBuilder

Dim i As Integer = 0
numMatches = json.SizeOfArray("match")
While i < numMatches

    json.I = i

    ' The replacement string for the first name will be all uppercase.
    json.J = firstNameIdx
    sbTemp.Clear()
    json.StringOfSb("match[i].group[j].cap",sbTemp)
    sbTemp.ToUppercase()
    json.UpdateSb("match[i].group[j].rep",sbTemp)

    ' Append "on" to the last name.
    json.J = lastNameIdx
    sbTemp.Clear()
    json.StringOfSb("match[i].group[j].cap",sbTemp)
    sbTemp.Append("on")
    json.UpdateSb("match[i].group[j].rep",sbTemp)

    i = i + 1
End While

' The JSON now has replacement strings:
Debug.WriteLine(json.Emit())

' {
'   "named": {
'     "first": 1,
'     "last": 2
'   },
'   "match": [
'     {
'       "group": [
'         {
'           "cap": "John Anders",
'           "idx": 0,
'           "len": 11
'         },
'         {
'           "cap": "John",
'           "idx": 0,
'           "len": 4,
'           "rep": "JOHN"
'         },
'         {
'           "cap": "Anders",
'           "idx": 5,
'           "len": 6,
'           "rep": "Anderson"
'         }
'       ]
'     },
'     {
'       "group": [
'         {
'           "cap": "Mary Robins",
'           "idx": 19,
'           "len": 11
'         },
'         {
'           "cap": "Mary",
'           "idx": 19,
'           "len": 4,
'           "rep": "MARY"
'         },
'         {
'           "cap": "Robins",
'           "idx": 24,
'           "len": 6,
'           "rep": "Robinson"
'         }
'       ]
'     }
'   ]
' }

' Call RegexReplace to update the StringBuilder with the replacements.
success = sb.RegexReplace(json)
If (success = False) Then
    Debug.WriteLine(sb.LastErrorText)
    Exit Sub
End If


Debug.WriteLine("Result after doing replacements:")
Debug.WriteLine(sb.GetAsString())

' Result after doing replacements:
' JOHN Anderson, +_+_+ MARY Robinson $$$$