Tcl

Regular Expression with Named Capture Groups

See more Regular Expressions Examples

Demonstrates regular expressions with named capture groups.

See the sample code below.

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

In PCRE2, named capture groups allow you to assign a name to a capturing group, making it easier to reference by name instead of number.

Syntax

(?<name>pattern)

or

(?'name'pattern)

Example

(?<first>\w+)\s+(?<last>\w+)

Applied to:

"John Smith"

Produces:

• first: John
• last: Smith

Tcl

load ./chilkat.dll

set success 0

set subject "John Smith"
set pattern "(?<first>\\w+)\\s+(?<last>\\w+)"

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]

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

# {
#   "named": {
#     "first": 1,
#     "last": 2
#   },
#   "match": [
#     {
#       "group": [
#         {
#           "cap": "John Smith",
#           "idx": 0,
#           "len": 10
#         },
#         {
#           "cap": "John",
#           "idx": 0,
#           "len": 4
#         },
#         {
#           "cap": "Smith",
#           "idx": 5,
#           "len": 5
#         }
#       ]
#     }
#   ]
# }

# The capture group index is obtained by looking up the name in the JSON result.
# For example:

CkJsonObject_put_I $json [CkJsonObject_IntOf $json "named.first"]
puts "first: [CkJsonObject_stringOf $json {match[0].group[i].cap}]"

CkJsonObject_put_I $json [CkJsonObject_IntOf $json "named.last"]
puts "last: [CkJsonObject_stringOf $json {match[0].group[i].cap}]"

# Output is: 

# first: John
# last: Smith

delete_CkStringBuilder $sb
delete_CkJsonObject $json