Go

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

Go

    success := false

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

    sb := chilkat.NewStringBuilder()
    sb.Append(subject)

    json := chilkat.NewJsonObject()
    json.SetEmitCompact(false)

    timeoutMs := 2000
    numMatches := sb.RegexMatch(pattern,json,timeoutMs)
    if numMatches < 0 {
        // Probably an error in the regular expression.
        // Suggestion: Use AI to help create and/or diagnose regular expressions.
        fmt.Println(sb.LastErrorText())
        sb.DisposeStringBuilder()
        json.DisposeJsonObject()
        return
    }

    // Examine the matches:
    fmt.Println(*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 $$$$

    firstNameIdx := json.IntOf("named.first")
    lastNameIdx := json.IntOf("named.last")

    sbTemp := chilkat.NewStringBuilder()

    i := 0
    numMatches = json.SizeOfArray("match")
    for i < numMatches {

        json.SetI(i)

        // The replacement string for the first name will be all uppercase.
        json.SetJ(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.SetJ(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
    }

    // The JSON now has replacement strings:
    fmt.Println(*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 {
        fmt.Println(sb.LastErrorText())
        sb.DisposeStringBuilder()
        json.DisposeJsonObject()
        sbTemp.DisposeStringBuilder()
        return
    }

    fmt.Println("Result after doing replacements:")
    fmt.Println(*sb.GetAsString())

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

    sb.DisposeStringBuilder()
    json.DisposeJsonObject()
    sbTemp.DisposeStringBuilder()