Ruby Trivia 3

Presented at the Berlin Ruby User Group (RUG::B) on November 5, 2015.

Transcript

1. Ruby Trivia 3
2. What is the value of the global variable $_? Question 1:
3. The String last read by gets. Answer 1:
4. How can you list all
 global variables? Bonus Question:
5. How can you list all
 global variables? Bonus Question: Answer: Use the Kernel#global_variables method.
6. How many global variables does Ruby define? global_variables.count Bonus Question:
7. How many global variables does Ruby define? global_variables.count Bonus Question: Answer: 54.
8. What does Ruby’s -n switch do? Question 2:
9. Causes Ruby to assume the following loop around your script, which makes it iterate over file name arguments like sed -n or awk. while gets ... end Answer 2:
10. What does Ruby’s -p switch do? Bonus Question:
11. Acts like the -n switch, but prints the value of variable $_ at the each end of the loop. For example: ruby -p -e '$_.tr! "a-z", "A-Z"' < file Bonus Question:
12. What thread-local variable can only store four possible values? Question 3:
13. What thread-local variable can only store four possible values? Question 3: Hint #1: Those values are 0, 1, 2, and 3.
14. What thread-local variable can only store four possible values? Question 3: Hint #1: Those values are 0, 1, 2, and 3. Hint #2: The value is 0 by default and can only increase.
15. $SAFE Answer 3: Trick question because it looks like a global variable, even though it behaves like a thread-local variable.
16. $SAFE Answer 3: There used to be $SAFE = 4 but it was removed in Ruby 2.1. Supposedly, it was only ever used by one company in Japan.
17. How can you check if an object is trusted? Bonus Question:
18. How can you check if an object is trusted? Bonus Question: Answer: Use the Kernel#tainted? method.
19. What happens if you do this? module Kernel def tainted? return false end end Question 4:
20. The tainted? method will always return false, but Ruby will still track tainted state via an internal FL_TAINT flag. Answer 4:
21. How can you mark a
 tainted object as safe? Question 5:
22. Kernel#untaint a.k.a. Kernel#trust $SAFE = 1 foo = gets.trust eval(foo) Answer 5:
23. Thanks for playing! Follow @sferik on Twitter for more Ruby trivia and practica.