The command may be executed when the value passed to Pathname is the first character of "|".
This is the same problem as https://bugs.ruby-lang.org/issues/14245, but here it is executed without warning.
```ruby
$ ruby -v
ruby 2.5.3p105 (2018-10-18 revision 65156) [x86_64-darwin16]
$ irb
irb(main)…