Searching for multiple elements with regex

Question

How can I check for a variable number of elements in a string?

[keyword1|keyword2|keyword3]
[keyword1|keyword2]

... or more than three keywords. This would just work for three elements:

preg_match("/^\[(.*)\|(.*)\|(.*)\]$/",$string, $matches)

Edit: How can I get the captured keyword in variables? i.e.:

matches[1] = keyword1
matches[2] = keyword2
matches[3] = keyword3

You'll need two separate patterns, one to validate the string, and one to extract the keywords. — Aran-Fey
– Aran-Fey, Commented Dec 26, 2014 at 16:12
@AvinashRaj: Variable Number, that means 1 or more keyword in that string (beginning with [ and ending with ]) — user3142695
– user3142695, Commented Dec 26, 2014 at 16:13

Community · Accepted Answer · 2017-05-23 12:28:27Z

2

You can use:

(?:^\[(?=[^][|]*(?:\|[^][|]*)*\])|(?!^)\G)([^][|]*)(?:[]|])

Regular expression visualization

DEMO

This technique is explained in details HERE

edited May 23, 2017 at 12:28

CommunityBot

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answered Dec 26, 2014 at 16:16

Enissay

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2 Comments

Enissay Over a year ago

@user3142695 It looks scary, but once you read the doc (link above) you'll see how much it's simple :)

Enissay Over a year ago

@AvinashRaj it's true that the (?=...) is not needed here, it only controls how many results to grab... Removing it will give a similar pattern to yours, so I'll leave it

Avinash Raj · Accepted Answer · 2014-12-26 16:35:12Z

1

Use this, 3 and more.

^\[[^|\n]*(?:\|[^|\n]*){2,}\]$

DEMO

FOr more than 3,

^\[[^|\n]*(?:\|[^|\n]*){3,}]$

DEMO

You could do simply like this through \G anchor,

(?:^\[|\G)\|?([^\n|\]]+)(?=[\]|])

Use \G anchor to do a continuous string match.

DEMO

edited Dec 26, 2014 at 16:35

answered Dec 26, 2014 at 16:02

Avinash Raj

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5 Comments

user3142695 Over a year ago

preg_match("/^\[[^|\n]*(?:\|[^|\n]*){2,}\]$/",$string, $matches) So my result would be: $matches[1], $matches[2], ... $matches[n]. Correct?

Avinash Raj Over a year ago

no, it matches that particular line only. Did you want to capture the keywords? Could you edit the question with expected output?

user3142695 Over a year ago

Yes, sorry for the unsufficient question. Updated the question.

user3142695 Over a year ago

In the regex101.com-link every second result is empty? match1 = 'keyword 1', match2 = '' and so on...

Avinash Raj Over a year ago

I think you could filter out the empty strings from an array easily.

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