putc(p1)
If obj is Numeric, write the character whose code is the least-significant byte of obj. If obj is String, write the first character of obj to ios. Otherwise, raise TypeError.
$stdout.putc "A" $stdout.putc 65
produces:
AA
static VALUE rb_io_putc(VALUE io, VALUE ch) { VALUE str; if (RB_TYPE_P(ch, T_STRING)) { str = rb_str_substr(ch, 0, 1); } else { char c = NUM2CHR(ch); str = rb_str_new(&c, 1); } rb_io_write(io, str); return ch; }