CODEWITHSUNDEEP
regex
vwoo
vwoo

Reputation:

regular expressions: match x times OR y times

Lets say I need to match a pattern if it appears 3 or 6 times in a row. The closest I can get is something like \d{3,6} but that doesn't quite do what I need.

'123' should match
'123456' should match
'1234' should not match

Upvotes: 36

Views: 72317

Answers (4)

CTS_AE
CTS_AE

Reputation: 14893

For this case we can get away with this crafty method:

Clean Implementation

/(\d{3}){1,2}/
/(?:\d{3}){1,2}/

How?!

This works because we're looking for multiples of three that are consecutive in this case.

Note: There's no reason to capture the group for this case so I add the ?: non capture group flag to the capture group.

This is similar to paxdiablo implementation, but slightly cleaner.

Matching Hex

I was doing something similar for matching on basic hex colors since they could be 3 or 6 in length. This allowed me to keep my hex color checker's matching DRY'd up ie: 

/^0x(?:[\da-f]{3}){1,2}$/i

Upvotes: 5

cletus
cletus

Reputation: 625297

^(\d{3}|\d{6})$

You have to have some sort of terminator otherwise \d{3} will match 1234. That's why I put ^ and $ above. One alternative is to use lookarounds:

(?<!\d)(\d{3}|\d{6})(?!\d)

to make sure it's not preceded by or followed by a digit (in this case). More in Lookahead and Lookbehind Zero-Width Assertions.

Upvotes: 45

Sean Owen
Sean Owen

Reputation: 66881

First one matches 3, 6 but also 9, 12, 15, .... Second looks right. Here's one more twist:

\d{3}\d{3}?

Upvotes: 0

paxdiablo
paxdiablo

Reputation: 882196

How about:

(\d\d\d){1,2}

although you'll also need guards at either end which depend on your RE engine, something like:

[^\d](\d\d\d){1,2}[^\d]

or:

^(\d\d\d){1,2}$

Upvotes: 17

Related Questions