How to Use AND in Ruby Regex

Question

I'm having problems with Ruby regex.

How do you do AND(&) regex in ruby?

ex:

cat and dog
cat
dog

I just want to match "cat and dog"

Answer 1

You can do something like a AND using positive look aheads

(?=.*cat)(?=.*dog).*

See it here on Rubular Updated link!

This positive lookahead (?=.*cat) checks if there is "cat" somewhere within the string, then the same is done for "dog" using (?=.*dog). If those both assertions are true then the complete string is matched with the .* at the end.

The advantage is that it will also match

dog and cat

and not only

cat and dog

but it will also match

dogs and cats

if you want exact matches, then use this

(?=.*\bcat\b)(?=.*\bdog\b).*

\b is a word boundary, i.e. it matches between a word and a non word character.

See it here

Answer 2

Your question is not very clear.

If you wish to match only those strings which contain both "cat" and "dog" (maybe as parts of a word), you could do:

/^.*(cat.*dog|dog.*cat).*$/

The above regex will match "concatenation dogma", but not "concatenation".

If you want to ensure that "cat" and "dog" appear as words by themselves, do:

/^.*(\bcat\b.*\bdog\b|\bdog\b.*\bcat\b).*$/

The above regex will match "cat and dog", but not "concatenation dogma" or "cat dogma".

Source: http://ruby-doc.org/docs/ProgrammingRuby/html/intro.html#S5