Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
Ruby Trivia 3
Search
Erik Berlin
December 03, 2015
Programming
0
700
Ruby Trivia 3
Presented at the Berlin Ruby User Group (RUG::B) on November 5, 2015.
Erik Berlin
December 03, 2015
Tweet
Share
More Decks by Erik Berlin
See All by Erik Berlin
Enumerator::Lazy
sferik
2
570
The Value of Being Lazy
sferik
3
780
Ruby Trivia 2
sferik
0
760
Ruby Trivia
sferik
2
1.3k
💀 Symbols
sferik
5
1.9k
Content Negotiation for REST APIs
sferik
8
1k
Writing Fast Ruby
sferik
628
62k
Mutation Testing with Mutant
sferik
5
1.1k
Other Decks in Programming
See All in Programming
リバースエンジニアリング新時代へ! GhidraとClaude DesktopをMCPで繋ぐ/findy202507
tkmru
4
1.2k
効率的な開発手段として VRTを活用する
ishkawa
1
180
「App Intent」よくわからんけどすごい!
rinngo0302
1
120
Git Sync を超える!OSS で実現する CDK Pull 型デプロイ / Deploying CDK with PipeCD in Pull-style
tkikuc
4
450
iOS開発スターターキットの作り方
akidon0000
0
170
脱Riverpod?fqueryで考える、TanStack Queryライクなアーキテクチャの可能性
ostk0069
0
560
AIコーディングエージェント全社導入とセキュリティ対策
hikaruegashira
11
6.9k
猫と暮らす Google Nest Cam生活🐈 / WebRTC with Google Nest Cam
yutailang0119
0
180
中級グラフィックス入門~効率的なメッシュレット描画~
projectasura
2
1.2k
AWS Summit Japan 2024と2025の比較/はじめてのKiro、今あなたは岐路に立つ
satoshi256kbyte
1
240
MySQL9でベクトルカラム登場!PHP×AWSでのAI/類似検索はこう変わる
suguruooki
1
220
MCPを使ってイベントソーシングのAIコーディングを効率化する / Streamlining Event Sourcing AI Coding with MCP
tomohisa
0
180
Featured
See All Featured
Side Projects
sachag
455
43k
Making Projects Easy
brettharned
116
6.3k
Building Flexible Design Systems
yeseniaperezcruz
328
39k
Fireside Chat
paigeccino
37
3.5k
Site-Speed That Sticks
csswizardry
10
710
Statistics for Hackers
jakevdp
799
220k
A better future with KSS
kneath
238
17k
I Don’t Have Time: Getting Over the Fear to Launch Your Podcast
jcasabona
33
2.4k
Product Roadmaps are Hard
iamctodd
PRO
54
11k
How to train your dragon (web standard)
notwaldorf
96
6.1k
Visualization
eitanlees
146
16k
Stop Working from a Prison Cell
hatefulcrawdad
271
21k
Transcript
Ruby Trivia 3
What is the value of the global variable $_? Question
1:
The String last read by gets. Answer 1:
How can you list all global variables? Bonus Question:
How can you list all global variables? Bonus Question: Answer:
Use the Kernel#global_variables method.
How many global variables does Ruby define? global_variables.count Bonus Question:
How many global variables does Ruby define? global_variables.count Bonus Question:
Answer: 54.
What does Ruby’s -n switch do? Question 2:
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:
What does Ruby’s -p switch do? Bonus Question:
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:
What thread-local variable can only store four possible values? Question
3:
What thread-local variable can only store four possible values? Question
3: Hint #1: Those values are 0, 1, 2, and 3.
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.
$SAFE Answer 3: Trick question because it looks like a
global variable, even though it behaves like a thread-local variable.
$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.
How can you check if an object is trusted? Bonus
Question:
How can you check if an object is trusted? Bonus
Question: Answer: Use the Kernel#tainted? method.
What happens if you do this? module Kernel def tainted?
return false end end Question 4:
The tainted? method will always return false, but Ruby will
still track tainted state via an internal FL_TAINT flag. Answer 4:
How can you mark a tainted object as safe? Question
5:
Kernel#untaint a.k.a. Kernel#trust $SAFE = 1 foo = gets.trust eval(foo)
Answer 5:
Thanks for playing! Follow @sferik on Twitter for more Ruby
trivia and practica.