operator

if /hay/ =~ 'haystack'
  puts "There is hay in the word haystack"
end

Note: The order is significant. Though 'haystack' =~ /hay/ is in most cases an equivalent, side effects might differ:

• Strings captured from named capture groups are assigned to local variables only when Regexp#=~ is called (regexp =~ str);
• Since the right operand might be is an arbitrary object, for regexp =~ str there will be called either Regexp#=~ or String#=~.

Note that this does not return a true/false value, it instead returns either the index of the match if found, or nil if not found. Because all integers in ruby are truthy (including 0) and nil is falsy, this works. If you want a boolean value, use #=== as shown in another example.