# class MatchData

`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:

- `$~` is `Regexp.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.

### Public Instance Methods

mtch == mtch2 → true or false

Equality—Two matchdata are equal if their target strings, patterns, and matched positions are identical.

Alias for: eql?
mtch[i] → str or nil click to toggle source
mtch[start, length] → array
mtch[range] → array
mtch[name] → str or nil

Match Reference – `MatchData` acts as an array, and may be accessed using the normal array indexing techniques. `mtch[0]` is equivalent to the special variable `$&`, and returns the entire matched string. `mtch[1]`, `mtch[2]`, and so on return the values of the matched backreferences (portions of the pattern between parentheses).

    m = /(.)(.)(\d+)(\d)/.match("THX1138.")
    m          #=> #<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"]

    m = /(?<foo>a+)b/.match("ccaaab")
    m          #=> #<MatchData "aaab" foo:"aaa">
    m["foo"]   #=> "aaa"
    m[:foo]    #=> "aaa"

    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);
        }
    }

begin(n) → integer click to toggle source

Returns the offset of the start of the nth element of the match array in the string. n can be a string or symbol to reference a named capture.

    m = /(.)(.)(\d+)(\d)/.match("THX1138.")
    m.begin(0)       #=> 1
    m.begin(2)       #=> 2

    m = /(?<foo>.)(.)(?<bar>.)/.match("hoge")
    p m.begin(:foo)  #=> 0
    p m.begin(:bar)  #=> 2

    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 INT2FIX(RMATCH(match)->rmatch->char_offset[i].beg);
    }

captures → array click to toggle source

Returns the array of captures; equivalent to `mtch.to_a[1..-1]`.

    f1,f2,f3,f4 = /(.)(.)(\d+)(\d)/.match("THX1138.").captures
    f1    #=> "H"
    f2    #=> "X"
    f3    #=> "113"
    f4    #=> "8"

    static VALUE
    match_captures(VALUE match)
    {
        return match_array(match, 1);
    }

end(n) → integer click to toggle source

Returns the offset of the character immediately following the end of the nth element of the match array in the string. n can be a string or symbol to reference a named capture.

    m = /(.)(.)(\d+)(\d)/.match("THX1138.")
    m.end(0)         #=> 7
    m.end(2)         #=> 3

    m = /(?<foo>.)(.)(?<bar>.)/.match("hoge")
    p m.end(:foo)    #=> 1
    p m.end(:bar)    #=> 3

    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 INT2FIX(RMATCH(match)->rmatch->char_offset[i].end);
    }

eql?(mtch2) → true or false click to toggle source

Equality—Two matchdata are equal if their target strings, patterns, and matched positions are identical.

    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;
    }

Also aliased as: ==
hash → integer click to toggle source

Produce a hash based on the target string, regexp and matched positions of this matchdata.

See also `Object#hash`.

    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);
    }

inspect → str click to toggle source

Returns a printable version of mtch.

    puts /.$/.match("foo").inspect
    #=> #<MatchData "o">

    puts /(.)(.)(.)/.match("foo").inspect
    #=> #<MatchData "foo" 1:"f" 2:"o" 3:"o">

    puts /(.)(.)?(.)/.match("fo").inspect
    #=> #<MatchData "fo" 1:"f" 2:nil 3:"o">

    puts /(?<foo>.)(?<bar>.)(?<baz>.)/.match("hoge").inspect
    #=> #<MatchData "hog" foo:"h" bar:"o" baz:"g">

    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

Returns the number of elements in the match array.

    m = /(.)(.)(\d+)(\d)/.match("THX1138.")
    m.length   #=> 5
    m.size     #=> 5

Alias for: size
match(n) → string or nil click to toggle source

Returns the captured substring corresponding to the argument. n can be a string or symbol to reference a named capture.

    m = /(.)(.)(\d+)(\d)(\w)?/.match("THX1138.")
    m.match(0)       #=> "HX1138"
    m.match(4)       #=> "8"
    m.match(5)       #=> nil

    m = /(?<foo>.)(.)(?<bar>.+)/.match("hoge")
    m.match(:foo)    #=> "h"
    m.match(:bar)    #=> "ge"

    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);
    }

match_length(n) → array click to toggle source

Returns the length of the captured substring corresponding to the argument. n can be a string or symbol to reference a named capture.

    m = /(.)(.)(\d+)(\d)(\w)?/.match("THX1138.")
    m.match_length(0)       #=> 6
    m.match_length(4)       #=> 1
    m.match_length(5)       #=> nil

    m = /(?<foo>.)(.)(?<bar>.+)/.match("hoge")
    m.match_length(:foo)    #=> 1
    m.match_length(:bar)    #=> 2

    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(match)->rmatch->char_offset[i];
        return LONG2NUM(ofs->end - ofs->beg);
    }

named_captures → hash click to toggle source

Returns a `Hash` using named capture.

A key of the hash is a name of the named captures. A value of the hash is a string of last successful capture of corresponding group.

    m = /(?<a>.)(?<b>.)/.match("01")
    m.named_captures #=> {"a" => "0", "b" => "1"}

    m = /(?<a>.)(?<b>.)?/.match("0")
    m.named_captures #=> {"a" => "0", "b" => nil}

    m = /(?<a>.)(?<a>.)/.match("01")
    m.named_captures #=> {"a" => "1"}

    m = /(?<a>x)|(?<a>y)/.match("x")
    m.named_captures #=> {"a" => "x"}

    static VALUE
    match_named_captures(VALUE match)
    {
        VALUE hash;
        struct MEMO *memo;

        match_check(match);
        if (NIL_P(RMATCH(match)->regexp))
            return rb_hash_new();

        hash = rb_hash_new();
        memo = MEMO_NEW(hash, match, 0);

        onig_foreach_name(RREGEXP(RMATCH(match)->regexp)->ptr, match_named_captures_iter, (void*)memo);

        return hash;
    }

names → [name1, name2, ...] click to toggle source

Returns a list of names of captures as an array of strings. This is the same as mtch.regexp.names.

    /(?<foo>.)(?<bar>.)(?<baz>.)/.match("hoge").names
    #=> ["foo", "bar", "baz"]

    m = /(?<x>.)(?<y>.)?/.match("a") #=> #<MatchData "a" x:"a" y:nil>
    m.names                          #=> ["x", "y"]

    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);
    }

offset(n) → array click to toggle source

Returns a two-element array containing the beginning and ending offsets of the nth match. n can be a string or symbol to reference a named capture.

    m = /(.)(.)(\d+)(\d)/.match("THX1138.")
    m.offset(0)      #=> [1, 7]
    m.offset(4)      #=> [6, 7]

    m = /(?<foo>.)(.)(?<bar>.)/.match("hoge")
    p m.offset(:foo) #=> [0, 1]
    p m.offset(:bar) #=> [2, 3]

    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(INT2FIX(RMATCH(match)->rmatch->char_offset[i].beg),
                            INT2FIX(RMATCH(match)->rmatch->char_offset[i].end));
    }

post_match → str click to toggle source

Returns the portion of the original string after the current match. Equivalent to the special variable `$'`.

    m = /(.)(.)(\d+)(\d)/.match("THX1138: The Movie")
    m.post_match   #=> ": The Movie"

    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 → str click to toggle source

Returns the portion of the original string before the current match. Equivalent to the special variable `$``.

    m = /(.)(.)(\d+)(\d)/.match("THX1138.")
    m.pre_match   #=> "T"

    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 click to toggle source

Returns the regexp.

    m = /a.*b/.match("abc")
    m.regexp #=> /a.*b/

    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));
            RMATCH(match)->regexp = regexp;
        }
        return regexp;
    }

size → integer click to toggle source

Returns the number of elements in the match array.

    m = /(.)(.)(\d+)(\d)/.match("THX1138.")
    m.length   #=> 5
    m.size     #=> 5

    static VALUE
    match_size(VALUE match)
    {
        match_check(match);
        return INT2FIX(RMATCH_REGS(match)->num_regs);
    }

Also aliased as: length
string → str click to toggle source

Returns a frozen copy of the string passed in to `match`.

    m = /(.)(.)(\d+)(\d)/.match("THX1138.")
    m.string   #=> "THX1138."

    static VALUE
    match_string(VALUE match)
    {
        match_check(match);
        return RMATCH(match)->str;  /* str is frozen */
    }

to_a → anArray click to toggle source

Returns the array of matches.

    m = /(.)(.)(\d+)(\d)/.match("THX1138.")
    m.to_a   #=> ["HX1138", "H", "X", "113", "8"]

Because `to_a` is called when expanding `*`variable, there’s a useful assignment shortcut for extracting matched fields. This is slightly slower than accessing the fields directly (as an intermediate array is generated).

    all,f1,f2,f3 = * /(.)(.)(\d+)(\d)/.match("THX1138.")
    all   #=> "HX1138"
    f1    #=> "H"
    f2    #=> "X"
    f3    #=> "113"

    static VALUE
    match_to_a(VALUE match)
    {
        return match_array(match, 0);
    }

to_s → str click to toggle source

Returns the entire matched string.

    m = /(.)(.)(\d+)(\d)/.match("THX1138.")
    m.to_s   #=> "HX1138"

    static VALUE
    match_to_s(VALUE match)
    {
        VALUE str = rb_reg_last_match(match);

        match_check(match);
        if (NIL_P(str)) str = rb_str_new(0,0);
        return str;
    }

values_at(index, ...) → array click to toggle source

Uses each index to access the matching values, returning an array of the corresponding matches.

    m = /(.)(.)(\d+)(\d)/.match("THX1138: The Movie")
    m.to_a               #=> ["HX1138", "H", "X", "113", "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")
    m.to_a               #=> ["1 + 2", "1", "+", "2"]
    m.values_at(:a, :b, :op) #=> ["1", "2", "+"]

    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;
    }