How can I check whether a string is an integer in Ruby? [duplicate]

Question

I have a string "1234223" and I want to check whether the value is an integer/number.

How can I do that in one line?

I have tried

1 =~ /^\d+$/
 => nil

"1a" =~ /^\d+$/
 => nil

Both line are returning nil.

For me your solution works fine, it is just that in the first case you are running the regexp on an int and not a string. Try to change the first line to "1" =~ /^\d+$/ — hirolau
– hirolau, Commented Sep 17, 2013 at 14:58
Do you want any integer, or an integer that is within the range of a built-in numeric type? If the former use regex, if the later use type conversion with rescue. — Martin Kealey
– Martin Kealey, Commented Jun 24, 2023 at 2:06

Peter Mortensen · Accepted Answer · 2023-06-01 21:57:07Z

22

Use Integer("123") rescue nil.

edited Jun 1, 2023 at 21:57

Peter Mortensen

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answered Sep 17, 2013 at 11:24

Victor Moroz

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1 Comment

FireDragon Over a year ago

best answer in my opinion. simple. i don't know why people prefer using complex regex...

Todd A. Jacobs · Accepted Answer · 2018-05-02 10:13:00Z

20

If you're attempting to keep similar semantics to the original post, use either of the following:

"1234223" =~ /\A\d+\z/ ? true : false
#=> true

!!("1234223" =~ /\A\d+\z/)
#=> true

A more idiomatic construction using Ruby 2.4's new Regexp#match? method to return a Boolean result will also do the same thing, while also looking a bit cleaner too. For example:

"1234223".match? /\A\d+\z/
#=> true

edited May 2, 2018 at 10:13

answered Sep 17, 2013 at 9:24

Todd A. Jacobs

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3 Comments

Amit Kumar Gupta Over a year ago

Nice, but what about negative numbers?

Todd A. Jacobs Over a year ago

@AmitKumarGupta Not part of the OP's corpus. Simple questions get simple answers.

Martin Kealey Over a year ago

There might not be a negative number in the examples, but the headline question asks about integers, not whole numbers (or unsigned integers).

Sajan Chandran · Accepted Answer · 2013-09-17 09:25:07Z

2

You can use regex

"123".match(/\A[+-]?\d+?(\.\d+)?\Z/) == nil ? false : true

It will also check for decimals.

answered Sep 17, 2013 at 9:25

Sajan Chandran

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1 Comment

Amit Kumar Gupta Over a year ago

Nice, but why the \.? The question is about integers, not decimal numbers.

sawa · Accepted Answer · 2013-09-17 09:30:47Z

1

"1234223".tap{|s| break s.empty? || s =~ /\D/}.!

answered Sep 17, 2013 at 9:30

sawa

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