How could I check to see if a word exists in a string, and return false if it doesn't, in ruby?

Question

Say I have a string str = "Things to do: eat and sleep."

How could I check if "do: " exists in str, case insensitive?

Solution 1

Like this:

puts "yes" if str =~ /do:/i

To return a boolean value (from a method, presumably), compare the result of the match to nil:

def has_do(str)
    (str =~ /do:/i) != nil
end

Or, if you don’t like the != nil then you can use !~ instead of =~ and negate the result:

def has_do(str)
    not str !~ /do:/i
end

But I don’t really like double negations …

Solution 2

In ruby 1.9 you can do like this:

str.downcase.match("do: ") do   
  puts "yes" 
end

It's not exactly what you asked for, but I noticed a comment to another answer. If you don't mind using regular expressions when matching the string, perhaps there is a way to skip the downcase part to get case insensitivity.

For more info, see String#match

Solution 3

You could also do this:

str.downcase.include? "Some string".downcase

Solution 4

If all I'm looking for is a case=insensitive substring match I usually use:

str.downcase['do: ']

9 times out of 10 I don't care where in the string the match is, so this is nice and concise.

Here's what it looks like in IRB:

>> str = "Things to do: eat and sleep." #=> "Things to do: eat and sleep."
>> str.downcase['do: '] #=> "do: "
>> str.downcase['foobar'] #=> nil

Because it returns nil if there is no hit it works in conditionals too.

View more solutions

Comments

[oxo]

Would it be possible to do this in an if block? E.g. if str =~ /do: /i puts "yes" end

[Konrad Rudolph]

@oxo Yes of course. In fact, the first code is merely a shorthand of that.

[PJP]

"perhaps there is a way to skip the downcase part to get case insensitivity"? str.match(/do: /i)

[Michael Kohl]

There's also the good old !! trick to only get a boolean result: >> !!(str =~ /do:/i) #=> true and >> !!(str =~ /da:/i) #=> false.

[Jakob W]

@theTinMan Oh, and it was even in the first answer as well. Need to think better next time =)

[David J.]

Why do you need to force a boolean? In Ruby, any value can be treated as if it is truthy; e.g. true / false.

[David J.]

If you are running many regexs that are case-insensitive, it might be more efficient to downcase once and then use many case-sensitive regexs.

[Konrad Rudolph]

@David Because that’s what the OP wanted. Normally I’d just use the expression directly, of course (see first example). But since the OP explicitly mentioned getting a boolean I showed how to do that, too.