How to check whether a string contains a substring in Ruby

You can use the include? method:

my_string = "abcdefg"
if my_string.include? "cde"
   puts "String includes 'cde'"
end

If case is irrelevant, then a case-insensitive regular expression is a good solution:

'aBcDe' =~ /bcd/i  # evaluates as true

This will also work for multi-line strings.

See Ruby's Regexp class for more information.

You can also do this...

my_string = "Hello world"

if my_string["Hello"]
  puts 'It has "Hello"'
else
  puts 'No "Hello" found'
end

# => 'It has "Hello"'

This example uses Ruby's String #[] method.

Expanding on Clint Pachl's answer:

Regex matching in Ruby returns nil when the expression doesn't match. When it does, it returns the index of the character where the match happens. For example:

"foobar" =~ /bar/  # returns 3
"foobar" =~ /foo/  # returns 0
"foobar" =~ /zzz/  # returns nil

It's important to note that in Ruby only nil and the boolean expression false evaluate to false. Everything else, including an empty Array, empty Hash, or the Integer 0, evaluates to true.

That's why the /foo/ example above works, and why.

if "string" =~ /regex/

works as expected, only entering the 'true' part of the if block if a match occurred.

A more succinct idiom than the accepted answer above that's available in Rails (from 3.1.0 and above) is .in?:

my_string = "abcdefg"
if "cde".in? my_string
  puts "'cde' is in the String."
  puts "i.e. String includes 'cde'"
end

I also think it's more readable.

See the in? documentation for more information.

Note again that it's only available in Rails, and not pure Ruby.

Ternary way

my_string.include?('ahr') ? (puts 'String includes ahr') : (puts 'String does not include ahr')

OR

puts (my_string.include?('ahr') ? 'String includes ahr' : 'String not includes ahr')

You can use the String Element Reference method which is []

Inside the [] can either be a literal substring, an index, or a regex:

> s='abcdefg'
=> "abcdefg"
> s['a']
=> "a"
> s['z']
=> nil

Since nil is functionally the same as false and any substring returned from [] is true you can use the logic as if you use the method .include?:

0> if s[sub_s]
1>    puts "\"#{s}\" has \"#{sub_s}\""
1> else 
1*    puts "\"#{s}\" does not have \"#{sub_s}\""
1> end
"abcdefg" has "abc"

0> if s[sub_s]
1>    puts "\"#{s}\" has \"#{sub_s}\""
1> else 
1*    puts "\"#{s}\" does not have \"#{sub_s}\""
1> end
"abcdefg" does not have "xyz" 

Just make sure you don't confuse an index with a sub string:

> '123456790'[8]    # integer is eighth element, or '0'
=> "0"              # would test as 'true' in Ruby
> '123456790'['8']  
=> nil              # correct

You can also use a regex:

> s[/A/i]
=> "a"
> s[/A/]
=> nil

How to check whether a string contains a substring in Ruby?

When you say 'check', I assume you want a boolean returned in which case you may use String#match?. match? accepts strings or regexes as its first parameter, if it's the former then it's automatically converted to a regex. So your use case would be:

str = 'string'
str.match? 'strings' #=> false
str.match? 'string'  #=> true
str.match? 'strin'   #=> true
str.match? 'trin'    #=> true
str.match? 'tri'     #=> true

String#match? has the added benefit of an optional second argument which specifies an index from which to search the string. By default this is set to 0.

str.match? 'tri',0   #=> true
str.match? 'tri',1   #=> true
str.match? 'tri',2   #=> false

user_input = gets.chomp
user_input.downcase!

if user_input.include?('substring')
  # Do something
end

This will help you check if the string contains substring or not

puts "Enter a string"
user_input = gets.chomp  # Ex: Tommy
user_input.downcase!    #  tommy


if user_input.include?('s')
    puts "Found"
else
    puts "Not found"
end

In case you can not use one of the libs mentioned above, one could achieve the same with simple text search (this is ignoring cases because of downcase):

ADD_BUTTON_TEXTS = ["add to cart", "add to basket"].freeze
target_text = "AdD tO cArT"
ADD_BUTTON_TEXTS.each do |text|
  puts "Text was found" if target_text.downcase.include?(text)
end