End of Life Ruby 3.1 has reached end of life and gets no more fixes. Switch to Ruby 4.0 →

instance method · added in Ruby 3.1

MatchData#match_length

mtch.match_length(n) → array

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);
}

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

Example

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

Ruby version changes

3.1
- MatchData#match_length is added [Feature #18172]

See also #match #named_captures #length #names also in 4.1 · 4.0 · 3.4 · 3.3 · 3.2

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