[nix-shell:~]$ irb --version
irb 1.2.6 (2020-09-14)
[nix-shell:~]$ irb
irb(main):001:0> 5r
=> (5/1)
irb(main):002:0> 5r**2
=> (25/1)
irb(main):003:0> 5**2
=> 25
irb(main):004:0> 5.0**2
=> 25.0
irb(main):005:0> 5r**2r
=> (25/1)

[nix-shell:~]$ mirb --version
mruby 3.1.0 (2022-05-12)
[nix-shell:~]$ mirb
mirb - Embeddable Interactive Ruby Shell
> 5r
 => (5/1)
> 5r**2
undefined method '**' (NoMethodError)
> 5**2
 => 25
> 5.0**2
 => 25.0
> 5**2r
 => 25