Using regex in simple if statements?

Question

Instead of doing:

puts "what type of input?"
input = gets.chomp
if %W[Int INT i I Ints ints].include?(input) 
puts "enter int"
i = gets.to_i

I want to use regex to interpret string user input. For example,

puts "are you entering in a string, an int or a float?"
case gets
when /\A(string|s)\z/i
puts "enter in a string"
gets.chomp
when /\A(int|i)\z/i
puts "enter an int"
gets.to_i
when /\A(float|f)\z/i
puts "enter a float"
gets.to_f
end

What is the syntax in order to get the same result but using if statements instead of case statement?

s = gets.chomp; if s.match?(/\A(string|s)\z/i) ... or ...if s.match(/\A(string|s)\z/i) ... or if s =~ /\A(string|s)\z/i .... You want \z, not \Z, for the end-of-string anchor. — Cary Swoveland
– Cary Swoveland, Commented Feb 12, 2020 at 5:21
@CarySwoveland how come? They want indeed \Z to avoid the necessity to chomp upfront. — Aleksei Matiushkin
– Aleksei Matiushkin, Commented Feb 12, 2020 at 5:39
@AlekseiMatiushkin, I forgot about \Z, or perhaps never knew (no way to know which). — Cary Swoveland
– Cary Swoveland, Commented Feb 12, 2020 at 5:42
\A...\Z behaves more like ^...$ – both match before an optional line terminator. (which is rarely of interest) — Stefan
– Stefan, Commented Feb 12, 2020 at 7:54
BTW, why are you asking for an if equivalent for that case expression? Matching various patterns against a single object is a prime example of using case. — Stefan
– Stefan, Commented Feb 12, 2020 at 8:07

Aleksei Matiushkin · Accepted Answer · 2020-02-12 05:39:29Z

2

gets returns a string with a trailing carriage return. What you need is to match the ending against \Z, not \z.

puts "are you entering in a string, an int or a float?"
case gets
when /\As(tring)?\Z/i
puts "enter in a string"
gets.chomp
when /\Ai(nt)?\Z/i
puts "enter an int"
gets.to_i
when /\Af(loat)?\z/i
puts "enter a float"
gets.to_f
else puts "Didn’t work"
end

I also slightly updated regexps to clearly show the intent.

answered Feb 12, 2020 at 5:39

Aleksei Matiushkin

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1 Comment

3limin4t0r Over a year ago

"\Z - Matches end of string. If string ends with a newline, it matches just before newline" - Ruby Doc

user1934428 · Accepted Answer · 2020-02-12 07:51:31Z

1

If you want to turn your case into an if, you have to store the expression intended for the gets into a variable:

response=gets.chomp
if /..../ =~ response
   ...
elsif /.../ =~ response
   ....
....
else
   ...
end

answered Feb 12, 2020 at 7:51

user1934428

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2 Comments

Aleksei Matiushkin Over a year ago

Why would anyone sane want to turn a clean case into elsif spaghetti?

user1934428 Over a year ago

I don't know. I didn't say that it is a good idea. Just the OP wanted to know - maybe out of theoretical interest?

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