(Go) Regular Expression with Capture Groups

See more Regular Expressions Examples

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

Demonstrates the following PCRE2 regular expression:

See the sample code below.

Name:\s+(\w+)\s+(\w+),\s+Email:\s+(\S+)

And apply it to this string:

Name: John Smith, Email: john.smith@example.com

Regex Components Explained

Part	Meaning	Matched Text
"Name:"	Matches the literal text "Name:"	"Name:"
"\s+"	Matches one or more whitespace characters (spaces, tabs, etc.)	(space)
"(\w+)"	Capture Group 1: One or more word characters ("a-zA-Z0-9_")	"John"
"\s+"	More whitespace	(space)
"(\w+)"	Capture Group 2: Another word (the last name)	"Smith"
","	A literal comma	","
"\s+"	Whitespace again	(space)
"Email:"	Matches the literal "Email:"	"Email:"
"\s+"	Whitespace	(space)
"(\S+)"	Capture Group 3: One or more non-whitespace characters	"john.smith@example.com"

Matches for Your Example String

String:

"Name: John Smith, Email: john.smith@example.com"

Regex Match Groups:

Group	Captured Value
Group 1	"John"
Group 2	"Smith"
Group 3	"john.smith@example.com"

Notes on Character Classes

\w matches [a-zA-Z0-9_] — so it doesn’t include punctuation like a period.
\S matches any non-whitespace character, so it’s good for capturing an email.

Note: This example requires Chilkat v11.1.0 or greater.

For more information, see https://www.chilkatsoft.com/chilkat_pcre2.asp

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    success := false

    subject := "Name: John Smith, Email: john.smith@example.com"
    pattern := "Name:\\s+(\\w+)\\s+(\\w+),\\s+Email:\\s+(\\S+)"

    sb := StringBuilder_Ref.html">chilkat.NewStringBuilder()
    sb.Append(subject)

    json := JsonObject_Ref.html">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())

    // This is the JSON with the match information.
    // See the JSON parsing code below to get the matched capture group values.

    // Important:  Capture group 0 always contains the entire match — that is, the portion of the input string that matches the full regular expression.

    // {
    //   "match": [
    //     {
    //       "group": [
    //         {
    //           "cap": "Name: John Smith, Email: john.smith@example.com",
    //           "idx": 0,
    //           "len": 47
    //         },
    //         {
    //           "cap": "John",
    //           "idx": 6,
    //           "len": 4
    //         },
    //         {
    //           "cap": "Smith",
    //           "idx": 11,
    //           "len": 5
    //         },
    //         {
    //           "cap": "john.smith@example.com",
    //           "idx": 25,
    //           "len": 22
    //         }
    //       ]
    //     }
    //   ]
    // }

    var cap *string = new(string)
    i := 0
    matchCount := json.SizeOfArray("match")
    for i < matchCount {
        fmt.Println("Match ", i + 1, ":")
        json.SetI(i)
        j := 0
        numCaptureGroups := json.SizeOfArray("match[i].group")
        for j < numCaptureGroups {
            json.SetJ(j)
            cap = json.StringOf("match[i].group[j].cap")
            fmt.Println(j, ": ", *cap)
            j = j + 1
        }

        i = i + 1
    }

    // Capture group 0 always contains the entire match — that is, the portion of the input string that matches the full regular expression.

    // Output

    // Match 1:
    // 0: Name: John Smith, Email: john.smith@example.com
    // 1: John
    // 2: Smith
    // 3: john.smith@example.com

    sb.DisposeStringBuilder()
    json.DisposeJsonObject()