Regular Expressions: Is there an AND operator?

Question

Obviously, you can use the | (pipe?) to represent OR, but is there a way to represent AND as well?

Specifically, I'd like to match paragraphs of text that contain ALL of a certain phrase, but in no particular order.

Transcript

Do you mean that you want to find phrases in a text, where each such phrase is a valid permutation of the words in a given phrase? – Petrochemistry

I'm putting this up here because three or four answer ignore it. Lookahead doesn't match the same length for each clause, unless they end in $. One lookahead could match four characters, and another 6. For example, (?=a*)(?=aab) will match aabaaaaba – Supplemental

try using just the "space" character for "AND" operator. – Infringement

1. I'd like to match paragraphs of text. 2. Containing out-of-order text. Number 1 is open to interpretation. Number 2 can be done a couple of ways. Way 1: (?:(?:(?(1)(?!))\b(phrase1)\b.*?|(?(2)(?!))\b(phrase2)\b.*?)){2}, Way 2: (?=.*\bphrase1\b)(?=.*\bphrase2\b) where in this, the matching of the paragraph in this case is undefined until the definition of paragraph is formalized. – Automotive

"Specifically, I'd like to match paragraphs of text that contain ALL of a certain phrase, but in no particular order." This is not analogous to what | does, which makes the question confused. | checks whether either of two patterns are matched at the current position. It does not check whether the rest of the string contains at least one of those two things. The "and" counterpart would, then, check whether both patterns are matched at the current position; but you apparently want to search the string and check that all patterns are matched somewhere in there. – Hae

"I'd like to match paragraphs of text that contain ALL of a certain phrase, but in no particular order." What exactly does this mean? What is "in no particular order" - the words of the phrase? The characters? Something else? Then, are the matches of "all" those things supposed to be sequential? Can they be overlapping? Can they have other intervening text? The problem is not even remotely well posed. – Hae

Answer 1

Use a non-consuming regular expression.

The typical (i.e. Perl/Java) notation is:

(?=expr)

This means "match expr but after that continue matching at the original match-point."

You can do as many of these as you want, and this will be an "and." Example:

(?=match this expression)(?=match this too)(?=oh, and this)

You can even add capture groups inside the non-consuming expressions if you need to save some of the data therein.

Zinazinah

Do you just place them all in a row, no separators between them? i.e. (?=apple)(?=orange)(?=pear) – Transcript

Separators (or any characters) would indicate that those must exist before the next non-consuming group. – Demeter

Giving this a try...I don't think this is exactly what he means. – Demeter

perl -e "q{some stuff and things} =~ /(?=some)(?=stuff)(?=things)/ ? print 'yes' : print 'no'" prints 'no'. – Demeter

Thanks for the good comments; I've updated the answer to include examples. – Zinazinah

It should be mentioned that this particular example is called a positive lookahead assertion. It has other uses than "and". Note that the text isn't consumed. – Cramfull

Using (?=) like this results in a regex that can never succeed. But it is the conjunction analog to |. The OP is just wrong in what he thinks will solve his problem. – Petrochemistry

perl -e "q{some stuff and things} =~ /(?=.*some)(?=.*stuff)(?=.*things)/ ? print 'yes' : print 'no'" – Remotion

Can you please add some easy example in perl code in your answer? – Parrett

It worth to mention that lookahead is not supported in japavascript. – Xeres

@Petrochemistry incorrect, e.g. in JavaScript the following regex matches a string that contains at least one lowercase, uppercase AND number character: /(?=.*[a-z])(?=.*[A-Z])(?=.*[0-9])/ The key is to prefix the character classes with .* since the lookaheads don't move the position, and it would otherwise try to match all three at the first character (which would be impossible). – Obligation

@Obligation agreed – Xeres

what kind of regex MTAIL is using?? how to use AND in .mtail program – Aggappora

Sooo... For some reason, when using .* inside our group this works, but when passing spaces inside it, it does not - So the code /(?=Client One)(?=.*Cloud.*)/ does not work but /(?=.*Client.*)(?=.*Cloud.*)/ does... Can you edit your question and pass a example on how to pass multiple words and spaces inside the group, without needing to use .* ? (Don't know if it is possible...) @JasonCohen – Contradance

Answer 2

You need to use lookahead as some of the other responders have said, but the lookahead has to account for other characters between its target word and the current match position. For example:

(?=.*word1)(?=.*word2)(?=.*word3)

The .* in the first lookahead lets it match however many characters it needs to before it gets to "word1". Then the match position is reset and the second lookahead seeks out "word2". Reset again, and the final part matches "word3"; since it's the last word you're checking for, it isn't necessary that it be in a lookahead, but it doesn't hurt.

In order to match a whole paragraph, you need to anchor the regex at both ends and add a final .* to consume the remaining characters. Using Perl-style notation, that would be:

/^(?=.*word1)(?=.*word2)(?=.*word3).*$/m

The 'm' modifier is for multline mode; it lets the ^ and $ match at paragraph boundaries ("line boundaries" in regex-speak). It's essential in this case that you not use the 's' modifier, which lets the dot metacharacter match newlines as well as all other characters.

Finally, you want to make sure you're matching whole words and not just fragments of longer words, so you need to add word boundaries:

/^(?=.*\bword1\b)(?=.*\bword2\b)(?=.*\bword3\b).*$/m

Aeschines

Exactly right - there is a tutorial about this as well! ocpsoft.org/tutorials/regular-expressions/and-in-regex – Retroact

+1 for clear and succint answer showcasing one of the best uses for lookaheads (unlike uses such as a hack to count the percentage match of a password). :) – Penley

Is this supported in MySQL's regexp() ? – Amber

@Liam:. MySQL uses the POSIX ERE flavor, so no. It effectively sacrifices features in favor of performance, which seems reasonable to me. There's more information here. – Aeschines

replace .* with [\s\S]* in javascript if you have new lines as . in javascript's regex engine does not match new lines and cannot be made to with modifiers – Impatience

Beware that this could potentially put all of stress of CPU if you are using a lot of lookups on large data volume. – Alienation

Answer 3

Look at this example:

We have 2 regexps A and B and we want to match both of them, so in pseudo-code it looks like this:

pattern = "/A AND B/"

It can be written without using the AND operator like this:

pattern = "/NOT (NOT A OR NOT B)/"

in PCRE:

"/(^(^A|^B))/"

regexp_match(pattern,data)

Brass

That's true in terms of formal logic, but it's absolutely no help here. In regexes, NOT can be even more difficult to express than AND. – Aeschines

@marvin_dpr It worked for me in CMake while the other suggestion (?=expr) not. It seems to be implementation dependent. – Tedi

Doesn't ^ mean "beginning of string" in regex syntax? – Intravenous

In regex in general, ^ is negation only at the beginning of a character class. Unless CMake is doing something really funky (to the point where calling their pattern matching language "regex" could be regarded as misleading or incorrect) I'm guessing the fact that it worked for you was an isolated accident. – Me

How could happen that this absolutely wrong answer got so much upvotes?! In the /(^(^A|^B))/ PCRE, ^ would mean “start of line” instead of negation. Maybe one can get some luck with negative lookahead ((?!…), e.g. (?!(?!A)|(?!B))), but certainly not with ^. – Isagogics

Answer 4

The AND operator is implicit in the RegExp syntax.
The OR operator has instead to be specified with a pipe.
The following RegExp:

var re = /ab/;

means the letter a AND the letter b.
It also works with groups:

var re = /(co)(de)/;

it means the group co AND the group de.
Replacing the (implicit) AND with an OR would require the following lines:

var re = /a|b/;
var re = /(co)|(de)/;

Resorcinol

Unfortunately, this is not what the OP asked for. This finds anything in that order, whereas they wanted them in any order. Check out the answer by stackoverflow.com/users/20938/alan-moore below which is the correct one. – Perl

@Perl thanks for your point, you are right and I misundertsood the question from Hugoware, I focused particularly on his first sentence. The right answer is a proper use of the lookahead operator, as AlanMoore wrote. Anyhow I think someone may find my clarification useful, as is has been already upvoted, so I wouldn't throw everything away. Regards. – Resorcinol

"means the letter a AND the letter b" No, it doesn't; it means a immediately followed by b. |, by contrast, checks both patterns at the same position. The analogous version is to use lookaheads to test whether both patterns are matched; but then it isn't clear what the match should consist of. – Hae

Answer 5

You can do that with a regular expression but probably you'll want to some else. For example use several regexp and combine them in a if clause.

You can enumerate all possible permutations with a standard regexp, like this (matches a, b and c in any order):

(abc)|(bca)|(acb)|(bac)|(cab)|(cba)

However, this makes a very long and probably inefficient regexp, if you have more than couple terms.

If you are using some extended regexp version, like Perl's or Java's, they have better ways to do this. Other answers have suggested using positive lookahead operation.

Indican

I don't think your approach is more inefficient than 3 lookaheads with their catastrophic backtracking. Sure it is longer to write, but note that you can easily generate the pattern automatically. Note that you can improve it to fail quicker with a(bc|cb)|b(ac|ca)|c(ab|ba). And the most important, you can use it with all regex flavour. – Flavorsome

Answer 6

Is it not possible in your case to do the AND on several matching results? in pseudocode

regexp_match(pattern1, data) && regexp_match(pattern2, data) && ...

Lath

I'm in a situation where i have some code that is a data table of rules, with a single regex pattern match string to test the rule's validity. Moving to multiple tests isn't something I can do in my case, and commonly in other folks' cases as well! – Nason

@AlanWolfe I am handling exactly the same case now ... so have you figured out the proper approach to deal with the logical AND? – Xylophagous

Answer 7

Why not use awk?
with awk regex AND, OR matters is so simple

awk '/WORD1/ && /WORD2/ && /WORD3/' myfile

Canaletto

Answer 8

The order is always implied in the structure of the regular expression. To accomplish what you want, you'll have to match the input string multiple times against different expressions.

What you want to do is not possible with a single regexp.

Ema

It's not technically impossible, but not worthwhile to implement. I dunno why someone downvoted though... – Demeter

Probably because it's not only possible, it's simple, assuming your regex flavor supports lookaheads. And that's a good bet; most of today's major programming languages do support them. – Aeschines

Answer 9

If you use Perl regular expressions, you can use positive lookahead:

For example

(?=[1-9][0-9]{2})[0-9]*[05]\b

would be numbers greater than 100 and divisible by 5

Myke

Answer 10

In addition to the accepted answer

I will provide you with some practical examples that will get things more clear to some of You. For example lets say we have those three lines of text:

[12/Oct/2015:00:37:29 +0200] // only this + will get selected
[12/Oct/2015:00:37:x9 +0200]
[12/Oct/2015:00:37:29 +020x]

See demo here DEMO

What we want to do here is to select the + sign but only if it's after two numbers with a space and if it's before four numbers. Those are the only constraints. We would use this regular expression to achieve it:

'~(?<=\d{2} )\+(?=\d{4})~g'

Note if you separate the expression it will give you different results.

Or perhaps you want to select some text between tags... but not the tags! Then you could use:

'~(?<=<p>).*?(?=<\/p>)~g'

for this text:

<p>Hello !</p> <p>I wont select tags! Only text with in</p> 

See demo here DEMO

Rightminded

Which answer was the accepted answer? Please add a link to it for the future me. – Proust

Answer 11

You could pipe your output to another regex. Using grep, you could do this:

grep A | grep B

Impacted

Answer 12

((yes).*(no))|((no).*(yes))

Will match sentence having both yes and no at the same time, regardless the order in which they appear:

Do i like cookies? **Yes**, i do. But milk - **no**, definitely no.

**No**, you may not have my phone. **Yes**, you may go f yourself.

Will both match, ignoring case.

Pulsometer

Very efficient. – Saponin

Answer 13

Use AND outside the regular expression. In PHP lookahead operator did not not seem to work for me, instead I used this

if( preg_match("/^.{3,}$/",$pass1) && !preg_match("/\s{1}/",$pass1))
    return true;
else
    return false;

The above regex will match if the password length is 3 characters or more and there are no spaces in the password.

Weiweibel

Answer 14

Here is a possible "form" for "and" operator:

Take the following regex for an example:

If we want to match words without the "e" character, we could do this:

/\b[^\We]+\b/g

• \W means NOT a "word" character.
• ^\W means a "word" character.
• [^\We] means a "word" character, but not an "e".

see it in action: word without e

"and" Operator for Regular Expressions

I think this pattern can be used as an "and" operator for regular expressions.

In general, if:

• A = not a
• B = not b

then:

[^AB] = not(A or B) 
      = not(A) and not(B) 
      = a and b

Difference Set

So, if we want to implement the concept of difference set in regular expressions, we could do this:

a - b = a and not(b)
      = a and B
      = [^Ab]

Peralta

Answer 15

Common Situation:

In javascript You can do this:

If you wanna check if a password contains both miniscule and majuscule letters, use this:

passwordValue.search(/[a-z]/) !== -1 && passwordValue.search(/[A-Z]/) !== -1

This statement returns true if the password input contains both miniscule and majuscule letters, otherwise it returns false.

Chough