How is the AND/OR operator represented as in Regular Expressions?

258
votes

I'm currently programming a vocabulary algorithm that checks if a user has typed in the word correctly. I have the following situation: The correct solution for the word would be "part1, part2". The user should be able to enter either "part1" (answer 1), "part2" (answer 2) or "part1, part2" (answer 3). I now try to match the string given by the user with the following, automatically created, regex expression:

^(part1|part2)$

This only returns answer 1 and 2 as correct while answer 3 would be wrong. I'm now wondering whether there's an operator similar to | that says and/or instead of either...or.

May anyone help me solve this problem?

6
regexoperators
Regular expressions might not be the best solution for this. I'd use normal string methods. – Felix Kling
This problem is poorly specified. Why are you using pattern matching when all you need is an exact string comparison against a set of legal strings? Unless your regex compiler optimizes alternatives into an O(1) trie structure the way Perl’s does, you should probably be doing a test against hash membership instead. Other regex engines just aren’t very clever at this. – tchrist
@tchrist The use case could be a mongodb $or regex match – Nadir Abbas

6 Answers

324
votes

I'm going to assume you want to build a the regex dynamically to contain other words than part1 and part2, and that you want order not to matter. If so you can use something like this:

((^|, )(part1|part2|part3))+$

Positive matches:

part1
part2, part1
part1, part2, part3

Negative matches:

part1,           //with and without trailing spaces.
part3, part2, 
otherpart1
37
votes
'^(part1|part2|part1,part2)$'

does it work?

5
votes

Does this work without alternation?

^((part)1(, \22)?)?(part2)?$

or why not this?

^((part)1(, (\22))?)?(\4)?$

The first works for all conditions the second for all but part2(using GNU sed 4.1.5)

4
votes

Not an expert in regex, but you can do ^((part1|part2)|(part1, part2))$. In words: "part 1 or part2 or both"

2
votes

Or you can use this: 

^(?:part[12]|(part)1,\12)$
1
votes

use
if in vim:

:s/{\|}/"/g

will replace { and } on " so {lol} becomes "lol"