Tcl

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.

Tcl

load ./chilkat.dll

set success 0

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

set sb [new_CkStringBuilder]

CkStringBuilder_Append $sb $subject

set json [new_CkJsonObject]

CkJsonObject_put_EmitCompact $json 0

set timeoutMs 2000
set numMatches [CkStringBuilder_RegexMatch $sb $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.
    puts [CkStringBuilder_lastErrorText $sb]
    delete_CkStringBuilder $sb
    delete_CkJsonObject $json
    exit
}

# Examine the matches:
puts [CkJsonObject_emit $json]

# 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
#         }
#       ]
#     }
#   ]
# }

set i 0
set matchCount [CkJsonObject_SizeOfArray $json "match"]
while {$i < $matchCount} {
    puts "Match [expr $i + 1]:"
    CkJsonObject_put_I $json $i
    set j 0
    set numCaptureGroups [CkJsonObject_SizeOfArray $json "match[i].group"]
    while {$j < $numCaptureGroups} {
        CkJsonObject_put_J $json $j
        set cap [CkJsonObject_stringOf $json "match[i].group[j].cap"]
        puts "$j: $cap"
        set j [expr $j + 1]
    }
    set i [expr $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

delete_CkStringBuilder $sb
delete_CkJsonObject $json