Class: MatchData
Overview
MatchData encapsulates the result of matching a ::Regexp against string. It is returned by Regexp#match and String#match, and also stored in a global variable returned by Regexp.last_match.
Usage:
url = 'https://docs.ruby-lang.org/en/2.5.0/MatchData.html'
m = url.match(/(\d\.?)+/)   # => #<MatchData "2.5.0" 1:"0">
m.string                    # => "https://docs.ruby-lang.org/en/2.5.0/MatchData.html"
m.regexp                    # => /(\d\.?)+/
# entire matched substring:
m[0]                        # => "2.5.0"
# Working with unnamed captures
m = url.match(%r{([^/])/([^/])\.html$})
m.captures                  # => ["2.5.0", "MatchData"]
m[1]                        # => "2.5.0"
m.values_at(1, 2)           # => ["2.5.0", "MatchData"]
# Working with named captures
m = url.match(%r{(?<version>[^/])/(?<module>[^/])\.html$})
m.captures                  # => ["2.5.0", "MatchData"]
m.named_captures            # => {"version"=>"2.5.0", "module"=>"MatchData"}
m[:version]                 # => "2.5.0"
m.values_at(:version, :module)
                            # => ["2.5.0", "MatchData"]
# Numerical indexes are working, too
m[1]                        # => "2.5.0"
m.values_at(1, 2)           # => ["2.5.0", "MatchData"]Global variables equivalence
Parts of last MatchData (returned by Regexp.last_match) are also aliased as global variables:
- 
$~isRegexp.last_match;
- 
$&is Regexp.last_match[ 0 ];
- 
$1,$2, and so on are Regexp.last_match[ i ](captures by number);
- 
$`is Regexp.last_match.pre_match;
- 
$'is Regexp.last_match.post_match;
- 
$+is Regexp.last_match[ -1 ](the last capture).
See also “Special global variables” section in ::Regexp documentation.
Instance Method Summary
- 
    
      #==(object)  ⇒ Boolean 
      (also: #eql?)
    
    Returns trueifobjectis another MatchData object whose target string, regexp, match, and captures are the same asself,falseotherwise.
- #[](index) ⇒ String?
- 
    
      #begin(n)  ⇒ Integer 
    
    Returns the offset (in characters) of the beginning of the specified match. 
- 
    
      #bytebegin(n)  ⇒ Integer 
    
    Returns the offset (in bytes) of the beginning of the specified match. 
- 
    
      #byteend(n)  ⇒ Integer 
    
    Returns the offset (in bytes) of the end of the specified match. 
- 
    
      #byteoffset(n)  ⇒ Array 
    
    Returns a two-element array containing the beginning and ending byte-based offsets of the nth match. 
- 
    
      #captures  ⇒ Array 
      (also: #deconstruct)
    
    Returns the array of captures, which are all matches except m[0]:
- 
    
      #deconstruct  ⇒ Array 
    
    Alias for #captures. 
- 
    
      #deconstruct_keys(array_of_names)  ⇒ Hash 
    
    Returns a hash of the named captures for the given names. 
- 
    
      #end(n)  ⇒ Integer 
    
    Returns the offset (in characters) of the end of the specified match. 
- 
    
      #eql?(object)  ⇒ Boolean 
    
    Alias for #==. 
- 
    
      #hash  ⇒ Integer 
    
    Returns the integer hash value for self, based on the target string, regexp, match, and captures.
- 
    
      #inspect  ⇒ String 
    
    Returns a string representation of self:
- 
    
      #length  ⇒ Integer 
      (also: #size)
    
    Returns size of the match array: 
- 
    
      #match(n)  ⇒ String? 
    
    Returns the matched substring corresponding to the given argument. 
- 
    
      #match_length(n)  ⇒ Integer? 
    
    Returns the length (in characters) of the matched substring corresponding to the given argument. 
- 
    
      #named_captures(symbolize_names: false)  ⇒ Hash 
    
    Returns a hash of the named captures; each key is a capture name; each value is its captured string or nil:
- 
    
      #names  ⇒ array_of_names 
    
    Returns an array of the capture names (see Named Captures): 
- 
    
      #offset(n)  ⇒ Array, end_offset 
    
    Returns a 2-element array containing the beginning and ending offsets (in characters) of the specified match. 
- 
    
      #post_match  ⇒ String 
    
    Returns the substring of the target string from the end of the first match in self(that is,self[0]) to the end of the string; equivalent to regexp global variable$':
- 
    
      #pre_match  ⇒ String 
    
    Returns the substring of the target string from its beginning up to the first match in self(that is,self[0]); equivalent to regexp global variable$`:
- 
    
      #regexp  ⇒ Regexp 
    
    Returns the regexp that produced the match: 
- 
    
      #size  ⇒ Integer 
    
    Alias for #length. 
- 
    
      #string  ⇒ String 
    
    Returns the target string if it was frozen; otherwise, returns a frozen copy of the target string: 
- 
    
      #to_a  ⇒ Array 
    
    Returns the array of matches: 
- 
    
      #to_s  ⇒ String 
    
    Returns the matched string: 
- 
    
      #values_at(*indexes)  ⇒ Array 
    
    Returns match and captures at the given indexes, which may include any mixture of:
- #initialize_copy(orig) Internal use only
Instance Method Details
    #==(object)  ⇒ Boolean     Also known as: #eql?
  
Returns true if object is another MatchData object whose target string, regexp, match, and captures are the same as self, false otherwise.
# File 're.c', line 3583
static VALUE
match_equal(VALUE match1, VALUE match2)
{
    const struct re_registers *regs1, *regs2;
    if (match1 == match2) return Qtrue;
    if (!RB_TYPE_P(match2, T_MATCH)) return Qfalse;
    if (!RMATCH(match1)->regexp || !RMATCH(match2)->regexp) return Qfalse;
    if (!rb_str_equal(RMATCH(match1)->str, RMATCH(match2)->str)) return Qfalse;
    if (!rb_reg_equal(match_regexp(match1), match_regexp(match2))) return Qfalse;
    regs1 = RMATCH_REGS(match1);
    regs2 = RMATCH_REGS(match2);
    if (regs1->num_regs != regs2->num_regs) return Qfalse;
    if (memcmp(regs1->beg, regs2->beg, regs1->num_regs * sizeof(*regs1->beg))) return Qfalse;
    if (memcmp(regs1->end, regs2->end, regs1->num_regs * sizeof(*regs1->end))) return Qfalse;
    return Qtrue;
}
  When arguments index, +start and #length, or range are given, returns match and captures in the style of Array#[]:
m = /(.)(.)(\d+)(\d)/.match("THX1138.")
# => #<MatchData "HX1138" 1:"H" 2:"X" 3:"113" 4:"8">
m[0] # => "HX1138"
m[1, 2]  # => ["H", "X"]
m[1..3]  # => ["H", "X", "113"]
m[-3, 2] # => ["X", "113"]When string or symbol argument name is given, returns the matched substring for the given name:
m = /(?<foo>.)(.)(?<bar>.+)/.match("hoge")
# => #<MatchData "hoge" foo:"h" bar:"ge">
m['foo'] # => "h"
m[:]  # => "ge"If multiple captures have the same name, returns the last matched substring.
m = /(?<foo>.)(?<foo>.+)/.match("hoge")
# => #<MatchData "hoge" foo:"h" foo:"oge">
m[:foo] #=> "oge"
m = /\W(?<foo>.)|\w(?<foo>.)|(?<foo>.+)/.match("hoge")
#<MatchData "hoge" foo:nil foo:"oge" foo:nil>
m[:foo] #=> "oge"# File 're.c', line 2234
static VALUE
match_aref(int argc, VALUE *argv, VALUE match)
{
    VALUE idx, length;
    match_check(match);
    rb_scan_args(argc, argv, "11", &idx, &length);
    if (NIL_P(length)) {
        if (FIXNUM_P(idx)) {
            return rb_reg_nth_match(FIX2INT(idx), match);
        }
        else {
            int num = namev_to_backref_number(RMATCH_REGS(match), RMATCH(match)->regexp, idx);
            if (num >= 0) {
                return rb_reg_nth_match(num, match);
            }
            else {
                return match_ary_aref(match, idx, Qnil);
            }
        }
    }
    else {
        long beg = NUM2LONG(idx);
        long len = NUM2LONG(length);
        long num_regs = RMATCH_REGS(match)->num_regs;
        if (len < 0) {
            return Qnil;
        }
        if (beg < 0) {
            beg += num_regs;
            if (beg < 0) return Qnil;
        }
        else if (beg > num_regs) {
            return Qnil;
        }
        if (beg+len > num_regs) {
            len = num_regs - beg;
        }
        return match_ary_subseq(match, beg, len, Qnil);
    }
}
  Returns the offset (in characters) of the beginning of the specified match.
When non-negative integer argument n is given, returns the offset of the beginning of the nth match:
m = /(.)(.)(\d+)(\d)/.match("THX1138.")
# => #<MatchData "HX1138" 1:"H" 2:"X" 3:"113" 4:"8">
m[0]       # => "HX1138"
m.begin(0) # => 1
m[3]       # => "113"
m.begin(3) # => 3
m = /(т)(е)(с)/.match('тест')
# => #<MatchData "тес" 1:"т" 2:"е" 3:"с">
m[0]       # => "тес"
m.begin(0) # => 0
m[3]       # => "с"
m.begin(3) # => 2When string or symbol argument name is given, returns the offset of the beginning for the named match:
m = /(?<foo>.)(.)(?<bar>.)/.match("hoge")
# => #<MatchData "hog" foo:"h" bar:"g">
m[:foo]        # => "h"
m.begin('foo') # => 0
m[:]        # => "g"
m.begin(:)  # => 2Related: #end, #offset, #byteoffset.
# File 're.c', line 1356
static VALUE
match_begin(VALUE match, VALUE n)
{
    int i = match_backref_number(match, n);
    struct re_registers *regs = RMATCH_REGS(match);
    match_check(match);
    backref_number_check(regs, i);
    if (BEG(i) < 0)
        return Qnil;
    update_char_offset(match);
    return LONG2NUM(RMATCH_EXT(match)->char_offset[i].beg);
}
  Returns the offset (in bytes) of the beginning of the specified match.
When non-negative integer argument n is given, returns the offset of the beginning of the nth match:
m = /(.)(.)(\d+)(\d)/.match("THX1138.")
# => #<MatchData "HX1138" 1:"H" 2:"X" 3:"113" 4:"8">
m[0]       # => "HX1138"
m.bytebegin(0) # => 1
m[3]       # => "113"
m.bytebegin(3) # => 3
m = /(т)(е)(с)/.match('тест')
# => #<MatchData "тес" 1:"т" 2:"е" 3:"с">
m[0]       # => "тес"
m.bytebegin(0) # => 0
m[3]       # => "с"
m.bytebegin(3) # => 4When string or symbol argument name is given, returns the offset of the beginning for the named match:
m = /(?<foo>.)(.)(?<bar>.)/.match("hoge")
# => #<MatchData "hog" foo:"h" bar:"g">
m[:foo]        # => "h"
m.bytebegin('foo') # => 0
m[:]        # => "g"
m.bytebegin(:)  # => 2Related: #byteend, #byteoffset.
# File 're.c', line 1308
static VALUE
match_bytebegin(VALUE match, VALUE n)
{
    int i = match_backref_number(match, n);
    struct re_registers *regs = RMATCH_REGS(match);
    match_check(match);
    backref_number_check(regs, i);
    if (BEG(i) < 0)
        return Qnil;
    return LONG2NUM(BEG(i));
}
  Returns the offset (in bytes) of the end of the specified match.
When non-negative integer argument n is given, returns the offset of the end of the nth match:
m = /(.)(.)(\d+)(\d)/.match("THX1138.")
# => #<MatchData "HX1138" 1:"H" 2:"X" 3:"113" 4:"8">
m[0]     # => "HX1138"
m.byteend(0) # => 7
m[3]     # => "113"
m.byteend(3) # => 6
m = /(т)(е)(с)/.match('тест')
# => #<MatchData "тес" 1:"т" 2:"е" 3:"с">
m[0]     # => "тес"
m.byteend(0) # => 6
m[3]     # => "с"
m.byteend(3) # => 6When string or symbol argument name is given, returns the offset of the end for the named match:
m = /(?<foo>.)(.)(?<bar>.)/.match("hoge")
# => #<MatchData "hog" foo:"h" bar:"g">
m[:foo]      # => "h"
m.byteend('foo') # => 1
m[:]      # => "g"
m.byteend(:)  # => 3Related: #bytebegin, #byteoffset.
# File 're.c', line 1332
static VALUE
match_byteend(VALUE match, VALUE n)
{
    int i = match_backref_number(match, n);
    struct re_registers *regs = RMATCH_REGS(match);
    match_check(match);
    backref_number_check(regs, i);
    if (BEG(i) < 0)
        return Qnil;
    return LONG2NUM(END(i));
}
  #byteoffset(n) ⇒ Array
Returns a two-element array containing the beginning and ending byte-based offsets of the nth match. n can be a string or symbol to reference a named capture.
m = /(.)(.)(\d+)(\d)/.match("THX1138.")
m.byteoffset(0)      #=> [1, 7]
m.byteoffset(4)      #=> [6, 7]
m = /(?<foo>.)(.)(?<bar>.)/.match("hoge")
p m.byteoffset(:foo) #=> [0, 1]
p m.byteoffset(:) #=> [2, 3]# File 're.c', line 1284
static VALUE
match_byteoffset(VALUE match, VALUE n)
{
    int i = match_backref_number(match, n);
    struct re_registers *regs = RMATCH_REGS(match);
    match_check(match);
    backref_number_check(regs, i);
    if (BEG(i) < 0)
        return rb_assoc_new(Qnil, Qnil);
    return rb_assoc_new(LONG2NUM(BEG(i)), LONG2NUM(END(i)));
}
  #captures ⇒ Array Also known as: #deconstruct
# File 're.c', line 2122
static VALUE
match_captures(VALUE match)
{
    return match_array(match, 1);
}
  Alias for #captures.
#deconstruct_keys(array_of_names) ⇒ Hash
Returns a hash of the named captures for the given names.
m = /(?<hours>\d{2}):(?<minutes>\d{2}):(?<seconds>\d{2})/.match("18:37:22")
m.deconstruct_keys([:hours, :minutes]) # => {:hours => "18", :minutes => "37"}
m.deconstruct_keys(nil) # => {:hours => "18", :minutes => "37", :seconds => "22"}Returns an empty hash if no named captures were defined:
m = /(\d{2}):(\d{2}):(\d{2})/.match("18:37:22")
m.deconstruct_keys(nil) # => {}# File 're.c', line 2477
static VALUE
match_deconstruct_keys(VALUE match, VALUE keys)
{
    VALUE h;
    long i;
    match_check(match);
    if (NIL_P(RMATCH(match)->regexp)) {
        return rb_hash_new_with_size(0);
    }
    if (NIL_P(keys)) {
        h = rb_hash_new_with_size(onig_number_of_names(RREGEXP_PTR(RMATCH(match)->regexp)));
        struct MEMO *memo;
        memo = MEMO_NEW(h, match, 1);
        onig_foreach_name(RREGEXP_PTR(RMATCH(match)->regexp), match_named_captures_iter, (void*)memo);
        return h;
    }
    Check_Type(keys, T_ARRAY);
    if (onig_number_of_names(RREGEXP_PTR(RMATCH(match)->regexp)) < RARRAY_LEN(keys)) {
        return rb_hash_new_with_size(0);
    }
    h = rb_hash_new_with_size(RARRAY_LEN(keys));
    for (i=0; i<RARRAY_LEN(keys); i++) {
        VALUE key = RARRAY_AREF(keys, i);
        VALUE name;
        Check_Type(key, T_SYMBOL);
        name = rb_sym2str(key);
        int num = NAME_TO_NUMBER(RMATCH_REGS(match), RMATCH(match)->regexp, RMATCH(match)->regexp,
                         RSTRING_PTR(name), RSTRING_END(name));
        if (num >= 0) {
            rb_hash_aset(h, key, rb_reg_nth_match(num, match));
        }
        else {
            return h;
        }
    }
    return h;
}
  Returns the offset (in characters) of the end of the specified match.
When non-negative integer argument n is given, returns the offset of the end of the nth match:
m = /(.)(.)(\d+)(\d)/.match("THX1138.")
# => #<MatchData "HX1138" 1:"H" 2:"X" 3:"113" 4:"8">
m[0]     # => "HX1138"
m.end(0) # => 7
m[3]     # => "113"
m.end(3) # => 6
m = /(т)(е)(с)/.match('тест')
# => #<MatchData "тес" 1:"т" 2:"е" 3:"с">
m[0]     # => "тес"
m.end(0) # => 3
m[3]     # => "с"
m.end(3) # => 3When string or symbol argument name is given, returns the offset of the end for the named match:
m = /(?<foo>.)(.)(?<bar>.)/.match("hoge")
# => #<MatchData "hog" foo:"h" bar:"g">
m[:foo]      # => "h"
m.end('foo') # => 1
m[:]      # => "g"
m.end(:)  # => 3Related: #begin, #offset, #byteoffset.
# File 're.c', line 1382
static VALUE
match_end(VALUE match, VALUE n)
{
    int i = match_backref_number(match, n);
    struct re_registers *regs = RMATCH_REGS(match);
    match_check(match);
    backref_number_check(regs, i);
    if (BEG(i) < 0)
        return Qnil;
    update_char_offset(match);
    return LONG2NUM(RMATCH_EXT(match)->char_offset[i].end);
}
  
    
      #==(object)  ⇒ Boolean 
      #eql?(object)  ⇒ Boolean 
    
  
Boolean 
      #eql?(object)  ⇒ Boolean 
    Alias for #==.
#hash ⇒ Integer
Returns the integer hash value for self, based on the target string, regexp, match, and captures.
See also Object#hash.
# File 're.c', line 3557
static VALUE
match_hash(VALUE match)
{
    const struct re_registers *regs;
    st_index_t hashval;
    match_check(match);
    hashval = rb_hash_start(rb_str_hash(RMATCH(match)->str));
    hashval = rb_hash_uint(hashval, reg_hash(match_regexp(match)));
    regs = RMATCH_REGS(match);
    hashval = rb_hash_uint(hashval, regs->num_regs);
    hashval = rb_hash_uint(hashval, rb_memhash(regs->beg, regs->num_regs * sizeof(*regs->beg)));
    hashval = rb_hash_uint(hashval, rb_memhash(regs->end, regs->num_regs * sizeof(*regs->end)));
    hashval = rb_hash_end(hashval);
    return ST2FIX(hashval);
}
  #initialize_copy(orig)
# File 're.c', line 1088
static VALUE
match_init_copy(VALUE obj, VALUE orig)
{
    rb_matchext_t *rm;
    if (!OBJ_INIT_COPY(obj, orig)) return obj;
    RB_OBJ_WRITE(obj, &RMATCH(obj)->str, RMATCH(orig)->str);
    RB_OBJ_WRITE(obj, &RMATCH(obj)->regexp, RMATCH(orig)->regexp);
    rm = RMATCH_EXT(obj);
    if (rb_reg_region_copy(&rm->regs, RMATCH_REGS(orig)))
        rb_memerror();
    if (RMATCH_EXT(orig)->char_offset_num_allocated) {
        if (rm->char_offset_num_allocated < rm->regs.num_regs) {
            REALLOC_N(rm->char_offset, struct rmatch_offset, rm->regs.num_regs);
            rm->char_offset_num_allocated = rm->regs.num_regs;
        }
        MEMCPY(rm->char_offset, RMATCH_EXT(orig)->char_offset,
               struct rmatch_offset, rm->regs.num_regs);
        RB_GC_GUARD(orig);
    }
    return obj;
}
  #inspect ⇒ String
Returns a string representation of self:
m = /.$/.match("foo")
# => #<MatchData "o">
m.inspect # => "#<MatchData \"o\">"
m = /(.)(.)(.)/.match("foo")
# => #<MatchData "foo" 1:"f" 2:"o" 3:"o">
m.inspect # => "#<MatchData \"foo\" 1:\"f\" 2:\"o\
m = /(.)(.)?(.)/.match("fo")
# => #<MatchData "fo" 1:"f" 2:nil 3:"o">
m.inspect # => "#<MatchData \"fo\" 1:\"f\" 2:nil 3:\"o\">"Related: #to_s.
# File 're.c', line 2590
static VALUE
match_inspect(VALUE match)
{
    VALUE cname = rb_class_path(rb_obj_class(match));
    VALUE str;
    int i;
    struct re_registers *regs = RMATCH_REGS(match);
    int num_regs = regs->num_regs;
    struct backref_name_tag *names;
    VALUE regexp = RMATCH(match)->regexp;
    if (regexp == 0) {
        return rb_sprintf("#<%"PRIsVALUE":%p>", cname, (void*)match);
    }
    else if (NIL_P(regexp)) {
        return rb_sprintf("#<%"PRIsVALUE": %"PRIsVALUE">",
                          cname, rb_reg_nth_match(0, match));
    }
    names = ALLOCA_N(struct backref_name_tag, num_regs);
    MEMZERO(names, struct backref_name_tag, num_regs);
    onig_foreach_name(RREGEXP_PTR(regexp),
            match_inspect_name_iter, names);
    str = rb_str_buf_new2("#<");
    rb_str_append(str, cname);
    for (i = 0; i < num_regs; i++) {
        VALUE v;
        rb_str_buf_cat2(str, " ");
        if (0 < i) {
            if (names[i].name)
                rb_str_buf_cat(str, (const char *)names[i].name, names[i].len);
            else {
                rb_str_catf(str, "%d", i);
            }
            rb_str_buf_cat2(str, ":");
        }
        v = rb_reg_nth_match(i, match);
        if (NIL_P(v))
            rb_str_buf_cat2(str, "nil");
        else
            rb_str_buf_append(str, rb_str_inspect(v));
    }
    rb_str_buf_cat2(str, ">");
    return str;
}
  #length ⇒ Integer Also known as: #size
# File 're.c', line 1183
static VALUE
match_size(VALUE match)
{
    match_check(match);
    return INT2FIX(RMATCH_REGS(match)->num_regs);
}
  Returns the matched substring corresponding to the given argument.
When non-negative argument n is given, returns the matched substring for the nth match:
m = /(.)(.)(\d+)(\d)(\w)?/.match("THX1138.")
# => #<MatchData "HX1138" 1:"H" 2:"X" 3:"113" 4:"8" 5:nil>
m.match(0) # => "HX1138"
m.match(4) # => "8"
m.match(5) # => nilWhen string or symbol argument name is given, returns the matched substring for the given name:
m = /(?<foo>.)(.)(?<bar>.+)/.match("hoge")
# => #<MatchData "hoge" foo:"h" bar:"ge">
m.match('foo') # => "h"
m.match(:)  # => "ge"# File 're.c', line 1424
static VALUE
match_nth(VALUE match, VALUE n)
{
    int i = match_backref_number(match, n);
    struct re_registers *regs = RMATCH_REGS(match);
    backref_number_check(regs, i);
    long start = BEG(i), end = END(i);
    if (start < 0)
        return Qnil;
    return rb_str_subseq(RMATCH(match)->str, start, end - start);
}
  Returns the length (in characters) of the matched substring corresponding to the given argument.
When non-negative argument n is given, returns the length of the matched substring for the nth match:
m = /(.)(.)(\d+)(\d)(\w)?/.match("THX1138.")
# => #<MatchData "HX1138" 1:"H" 2:"X" 3:"113" 4:"8" 5:nil>
m.match_length(0) # => 6
m.match_length(4) # => 1
m.match_length(5) # => nilWhen string or symbol argument name is given, returns the length of the matched substring for the named match:
m = /(?<foo>.)(.)(?<bar>.+)/.match("hoge")
# => #<MatchData "hoge" foo:"h" bar:"ge">
m.match_length('foo') # => 1
m.match_length(:)  # => 2# File 're.c', line 1468
static VALUE
match_nth_length(VALUE match, VALUE n)
{
    int i = match_backref_number(match, n);
    struct re_registers *regs = RMATCH_REGS(match);
    match_check(match);
    backref_number_check(regs, i);
    if (BEG(i) < 0)
        return Qnil;
    update_char_offset(match);
    const struct rmatch_offset *const ofs =
        &RMATCH_EXT(match)->char_offset[i];
    return LONG2NUM(ofs->end - ofs->beg);
}
  #named_captures(symbolize_names: false) ⇒ Hash
Returns a hash of the named captures; each key is a capture name; each value is its captured string or nil:
m = /(?<foo>.)(.)(?<bar>.+)/.match("hoge")
# => #<MatchData "hoge" foo:"h" bar:"ge">
m.named_captures # => {"foo"=>"h", "bar"=>"ge"}
m = /(?<a>.)(?<b>.)/.match("01")
# => #<MatchData "01" a:"0" b:"1">
m.named_captures #=> {"a" => "0", "b" => "1"}
m = /(?<a>.)(?<b>.)?/.match("0")
# => #<MatchData "0" a:"0" b:nil>
m.named_captures #=> {"a" => "0", "b" => nil}
m = /(?<a>.)(?<a>.)/.match("01")
# => #<MatchData "01" a:"0" a:"1">
m.named_captures #=> {"a" => "1"}If keyword argument symbolize_names is given a true value, the keys in the resulting hash are Symbols:
m = /(?<a>.)(?<a>.)/.match("01")
# => #<MatchData "01" a:"0" a:"1">
m.named_captures(symbolize_names: true) #=> {:a => "1"}# File 're.c', line 2424
static VALUE
match_named_captures(int argc, VALUE *argv, VALUE match)
{
    VALUE hash;
    struct MEMO *memo;
    match_check(match);
    if (NIL_P(RMATCH(match)->regexp))
        return rb_hash_new();
    VALUE opt;
    VALUE symbolize_names = 0;
    rb_scan_args(argc, argv, "0:", &opt);
    if (!NIL_P(opt)) {
        static ID keyword_ids[1];
        VALUE symbolize_names_val;
        if (!keyword_ids[0]) {
            keyword_ids[0] = rb_intern_const("symbolize_names");
        }
        rb_get_kwargs(opt, keyword_ids, 0, 1, &symbolize_names_val);
        if (!UNDEF_P(symbolize_names_val) && RTEST(symbolize_names_val)) {
            symbolize_names = 1;
        }
    }
    hash = rb_hash_new();
    memo = MEMO_NEW(hash, match, symbolize_names);
    onig_foreach_name(RREGEXP(RMATCH(match)->regexp)->ptr, match_named_captures_iter, (void*)memo);
    return hash;
}
  
    #names  ⇒ array_of_names   
Returns an array of the capture names (see Named Captures):
m = /(?<foo>.)(?<bar>.)(?<baz>.)/.match("hoge")
# => #<MatchData "hog" foo:"h" bar:"o" baz:"g">
m.names # => ["foo", "bar", "baz"]
m = /foo/.match('foo') # => #<MatchData "foo">
m.names # => [] # No named captures.Equivalent to:
m = /(?<foo>.)(?<bar>.)(?<baz>.)/.match("hoge")
m.regexp.names # => ["foo", "bar", "baz"]# File 're.c', line 1162
static VALUE
match_names(VALUE match)
{
    match_check(match);
    if (NIL_P(RMATCH(match)->regexp))
        return rb_ary_new_capa(0);
    return rb_reg_names(RMATCH(match)->regexp);
}
  Returns a 2-element array containing the beginning and ending offsets (in characters) of the specified match.
When non-negative integer argument n is given, returns the starting and ending offsets of the nth match:
m = /(.)(.)(\d+)(\d)/.match("THX1138.")
# => #<MatchData "HX1138" 1:"H" 2:"X" 3:"113" 4:"8">
m[0]        # => "HX1138"
m.offset(0) # => [1, 7]
m[3]        # => "113"
m.offset(3) # => [3, 6]
m = /(т)(е)(с)/.match('тест')
# => #<MatchData "тес" 1:"т" 2:"е" 3:"с">
m[0]        # => "тес"
m.offset(0) # => [0, 3]
m[3]        # => "с"
m.offset(3) # => [2, 3]When string or symbol argument name is given, returns the starting and ending offsets for the named match:
m = /(?<foo>.)(.)(?<bar>.)/.match("hoge")
# => #<MatchData "hog" foo:"h" bar:"g">
m[:foo]         # => "h"
m.offset('foo') # => [0, 1]
m[:]         # => "g"
m.offset(:)  # => [2, 3]Related: #byteoffset, #begin, #end.
# File 're.c', line 1249
static VALUE
match_offset(VALUE match, VALUE n)
{
    int i = match_backref_number(match, n);
    struct re_registers *regs = RMATCH_REGS(match);
    match_check(match);
    backref_number_check(regs, i);
    if (BEG(i) < 0)
        return rb_assoc_new(Qnil, Qnil);
    update_char_offset(match);
    return rb_assoc_new(LONG2NUM(RMATCH_EXT(match)->char_offset[i].beg),
                        LONG2NUM(RMATCH_EXT(match)->char_offset[i].end));
}
  #post_match ⇒ String
Returns the substring of the target string from the end of the first match in self (that is, self[0]) to the end of the string; equivalent to regexp global variable $':
m = /(.)(.)(\d+)(\d)/.match("THX1138: The Movie")
# => #<MatchData "HX1138" 1:"H" 2:"X" 3:"113" 4:"8">
m[0]         # => "HX1138"
m.post_match # => ": The Movie"\Related: #pre_match.
# File 're.c', line 1986
VALUE
rb_reg_match_post(VALUE match)
{
    VALUE str;
    long pos;
    struct re_registers *regs;
    if (NIL_P(match)) return Qnil;
    match_check(match);
    regs = RMATCH_REGS(match);
    if (BEG(0) == -1) return Qnil;
    str = RMATCH(match)->str;
    pos = END(0);
    str = rb_str_subseq(str, pos, RSTRING_LEN(str) - pos);
    return str;
}
  #pre_match ⇒ String
Returns the substring of the target string from its beginning up to the first match in self (that is, self[0]); equivalent to regexp global variable $`:
m = /(.)(.)(\d+)(\d)/.match("THX1138.")
# => #<MatchData "HX1138" 1:"H" 2:"X" 3:"113" 4:"8">
m[0]        # => "HX1138"
m.pre_match # => "T"Related: #post_match.
# File 're.c', line 1953
VALUE
rb_reg_match_pre(VALUE match)
{
    VALUE str;
    struct re_registers *regs;
    if (NIL_P(match)) return Qnil;
    match_check(match);
    regs = RMATCH_REGS(match);
    if (BEG(0) == -1) return Qnil;
    str = rb_str_subseq(RMATCH(match)->str, 0, BEG(0));
    return str;
}
  #regexp ⇒ Regexp
Returns the regexp that produced the match:
m = /a.*b/.match("abc") # => #<MatchData "ab">
m.regexp                # => /a.*b/# File 're.c', line 1127
static VALUE
match_regexp(VALUE match)
{
    VALUE regexp;
    match_check(match);
    regexp = RMATCH(match)->regexp;
    if (NIL_P(regexp)) {
        VALUE str = rb_reg_nth_match(0, match);
        regexp = rb_reg_regcomp(rb_reg_quote(str));
        RB_OBJ_WRITE(match, &RMATCH(match)->regexp, regexp);
    }
    return regexp;
}
  Alias for #length.
#string ⇒ String
Returns the target string if it was frozen; otherwise, returns a frozen copy of the target string:
m = /(.)(.)(\d+)(\d)/.match("THX1138.")
# => #<MatchData "HX1138" 1:"H" 2:"X" 3:"113" 4:"8">
m.string # => "THX1138."# File 're.c', line 2543
static VALUE
match_string(VALUE match)
{
    match_check(match);
    return RMATCH(match)->str;	/* str is frozen */
}
  #to_a ⇒ Array
# File 're.c', line 2100
static VALUE
match_to_a(VALUE match)
{
    return match_array(match, 0);
}
  #to_s ⇒ String
# File 're.c', line 2348
static VALUE
match_to_s(VALUE match)
{
    VALUE str = rb_reg_last_match(match_check(match));
    if (NIL_P(str)) str = rb_str_new(0,0);
    return str;
}
  #values_at(*indexes) ⇒ Array
Returns match and captures at the given indexes, which may include any mixture of:
- 
Integers. 
- 
Ranges. 
- 
Names (strings and symbols). 
Examples:
m = /(.)(.)(\d+)(\d)/.match("THX1138: The Movie")
# => #<MatchData "HX1138" 1:"H" 2:"X" 3:"113" 4:"8">
m.values_at(0, 2, -2) # => ["HX1138", "X", "113"]
m.values_at(1..2, -1) # => ["H", "X", "8"]
m = /(?<a>\d+) *(?<op>[+\-*\/]) *(?<b>\d+)/.match("1 + 2")
# => #<MatchData "1 + 2" a:"1" op:"+" b:"2">
m.values_at(0, 1..2, :a, :b, :op)
# => ["1 + 2", "1", "+", "1", "2", "+"]# File 're.c', line 2303
static VALUE
match_values_at(int argc, VALUE *argv, VALUE match)
{
    VALUE result;
    int i;
    match_check(match);
    result = rb_ary_new2(argc);
    for (i=0; i<argc; i++) {
        if (FIXNUM_P(argv[i])) {
            rb_ary_push(result, rb_reg_nth_match(FIX2INT(argv[i]), match));
        }
        else {
            int num = namev_to_backref_number(RMATCH_REGS(match), RMATCH(match)->regexp, argv[i]);
            if (num >= 0) {
                rb_ary_push(result, rb_reg_nth_match(num, match));
            }
            else {
                match_ary_aref(match, argv[i], result);
            }
        }
    }
    return result;
}