Ruby longest word in txtfile

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Ruby

Im new to ruby, and have chosen a self learning course for expanding on current languages. I bought a book but the examples are so vague and badly written that you can pull nothing use full from copying them.

guys, below is a script for opening a file spliting the words and hashing them. then displaying how many times each word appears

words = File.open('my_text.txt') {|f| f.read }.split
freqs=Hash.new(0)
words.each { |word| freqs[word] += 1 }
freqs.sort_by {|x,y| y }.reverse.each {|w, f| puts w+' '+f.to_s}

what im trying to achieve is finding the 'longest' word in this txt file, i just cant seem to do it, any suggestions or a point in the right direction please?

example from my book:

longest = %w{ cat sheep bear }.inject do |memo,word| memo.length > word.length ? memo : word

end

cannot put the hash into this, have tried multiple ways, it just throws errors