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

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, Sep 17 '13 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, Jun 24 '23 at 02:06

score 20 · Answer 1 · edited Jun 01 '23 at 21:57

20

Use Integer("123") rescue nil.

edited Jun 01 '23 at 21:57

Peter Mortensen

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answered Sep 17 '13 at 11:24

Victor Moroz

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best answer in my opinion. simple. i don't know why people prefer using complex regex... – FireDragon May 15 '19 at 22:36

Todd A. Jacobs · Accepted Answer · 2018-05-02T10:13:00.170

19

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 02 '18 at 10:13

answered Sep 17 '13 at 09:24

Todd A. Jacobs

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Nice, but what about negative numbers? – Amit Kumar Gupta Sep 17 '13 at 09:27
3

@AmitKumarGupta Not part of the OP's corpus. Simple questions get simple answers. – Todd A. Jacobs Sep 17 '13 at 09:29
2

There might not be a negative number in the examples, but the headline question asks about _integers_, not _whole numbers_ (or _unsigned integers_). – Martin Kealey Jun 24 '23 at 02:03

score 2 · Answer 3 · answered Sep 17 '13 at 09:25

2

You can use regex

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

It will also check for decimals.

answered Sep 17 '13 at 09:25

Sajan Chandran

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Nice, but why the `\.`? The question is about integers, not decimal numbers. – Amit Kumar Gupta Sep 17 '13 at 09:27

score 1 · Answer 4 · answered Sep 17 '13 at 09:30

1

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

answered Sep 17 '13 at 09:30

sawa

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

4 Answers4