When you need to use diff in either some Ruby code or your Rails app, use the differ gem Show archive.org snapshot .

puts Differ.diff "foo", "boo"
# => {"boo" >> "foo"}

Usage

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There are several variants available, all using the base method diff(to, from, separator = "\n").
You have diff_by_line, diff_by_word, diff_by_char and may of course use your own separator:

puts Differ.diff 'Hauptsatz, und mein Nebensatz.', 'Hauptsatz, und dein Nebensatz.', ','
# => Hauptsatz,{" und dein Nebensatz." >> " und mein Nebensatz."}

Formatting

Standard formatting is :ascii. You also have :html and :color formatting:

diff = Differ.diff "foo", "boo"

puts diff.format_as :html
# => <del class="differ">boo</del><ins class="differ">foo</ins>

puts diff.format_as :color
# => \e[31mboo\e[0m\e[32mfoo\e[0m
# In a terminal, this will be "boofoo" with boo being red and foo being green.

For more detailed information, check the attached link.