对异常$！使用Ruby全局变量 在铁轨上

Question

I'm trying to access the last exception_message from my rails app by using the ruby global variable $!, but it is coming back at nil despite multiple exceptions having occurred before the variable being called. Does this not work in rails? Is there another way to access the last exception that was raised in the application?

Answer 1

I'm not sure why $! always returns nil . As I wrote in the comment above, 0 / 0 rescue $! works but I can't seem to get it to work in any other context.

One way you can access the exception in a Ruby program is by using => after rescue like so:

[24] pry(main)> begin
[24] pry(main)*   undefined_variable
[24] pry(main)* rescue => e
[24] pry(main)*   puts e
[24] pry(main)* end
undefined local variable or method `undefined_variable' for main:Object
=> nil

Answer 2

It turns out that $! isn't all that global. It just works in the call stack of the exception - which I guess makes sense.

https://www.honeybadger.io/blog/working-with-ruby-exceptions-outside-of-the-rescue-block/

"This means that $! is pretty useless inside of a shell like IRB. Often in IRB, I'll run a method and get an exception. Sometimes I'd like to get ahold of that exception object. But $! doesn't work for this."