B4X Requires Chilkat v11.1.0+

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

B4X

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 ChilkatStringBuilder
sb.Initialize
sb.Append(subject)

Dim json As ChilkatJsonObject
json.Initialize
json.EmitCompact = False

Dim timeoutMs As Int = 2000
Dim numMatches As Int = 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.
    Log(sb.LastErrorText)
    Return
End If


'  Examine the matches:
Log(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 Int = json.IntOf("named.first")
Dim lastNameIdx As Int = json.IntOf("named.last")

Dim sbTemp As ChilkatStringBuilder
sbTemp.Initialize

Dim i As Int = 0
numMatches = json.SizeOfArray("match")
Do 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
Loop

'  The JSON now has replacement strings:
Log(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
    Log(sb.LastErrorText)
    Return
End If


Log("Result after doing replacements:")
Log(sb.GetAsString)

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