Boolean check if a string matches a regex in ruby?

Question

In ruby, I have seen a lot of code doing things like:

def test(s)
  s =~ /Macintosh/
end

to test whether or not a string matches a regex. However, this returns a fixnum or nil, depending on if it finds a match. Is there a way to do the same operation, but have it return a boolean as to whether or not it matched?

The two possible solutions that I thought of were !(s =~ /Macintosh/).nil? and !(s !~ /Macintosh/), but neither of those seem very readable. Is there something like:

def test(s)
  s.matches?(/Macintosh/)
end

@rathrio that would check and then check for nil, I'm asking if there's a boolean method that would return true or false. — kddeisz
– kddeisz, Commented Jan 28, 2014 at 21:38
Just out of interest: Is there a specific reason why you want a Boolean? In most use cases returning nil or a non-nil value would work just fine, right? — Radi
– Radi, Commented Jan 28, 2014 at 21:47
@rathrio The problem is, if the needle is at position 0 in the haystack, =~ returns 0. And while ruby evaluates 0 as true, mysql doesn't. It's a rails thing. — kddeisz
– kddeisz, Commented Jan 28, 2014 at 21:55

Casimir et Hippolyte · Accepted Answer · 2014-01-28 21:47:38Z

11

You can use this:

def test(s)
    /Macintosh/ === s
end

edited Jan 28, 2014 at 21:47

answered Jan 28, 2014 at 21:36

Casimir et Hippolyte

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4 Comments

kddeisz Over a year ago

The question is whether or not there exists a method that does a boolean check, without needing to check nil at the end. !! is the same as .nil?.

Casimir et Hippolyte Over a year ago

@kdeisz: where is the gift basket?

Saikat... Over a year ago

I am having a rubocop error for this... Avoid the use of the case equality operator(===). How can i use match method instead === ?

Darren Weber Over a year ago

BTW, it's good style to add a ? to a boolean method, as in test?(s).

Darren Weber · Accepted Answer · 2017-01-17 21:55:22Z

1

Ternary syntax might help or fit a different style preference:

x = '10.0.0'
x =~ /\d*\.\d*\.\d*/ ? true : false  # => true

# Unlike c-style languages, 0 is true in ruby:
x =~ /\d*\.\d*\.\d*/                 # => 0
0 ? true : false                     # => true

The order of the case compare operator === is important [1], e.g.:

/\d*\.\d*\.\d*/ === x
#=> true
x === /\d*\.\d*\.\d*/
#=> false

[1] https://ruby-doc.org/core-2.2.0/Regexp.html#method-i-3D-3D-3D

answered Jan 17, 2017 at 21:55

Darren Weber

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Comments

Ollie Bennett · Accepted Answer · 2022-03-15 14:01:55Z

0

Since Ruby 2.4.0, you can use Regexp#match which returns a boolean result;

/Macintosh/.match?(s)

answered Mar 15, 2022 at 14:01

Ollie Bennett

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