"Optional" substring matching with regex

Question

I am writing a regular expression in PHP that will need to extract data from strings that look like:

Naujasis Salemas, Šiaurės Dakota
Jungtinės Valstijos (Centras, Šiaurės Dakota)

I would like to extract:

Naujasis Salemas
Centras

For the first case, I have written [^-]*(?=,), which works quite well. I would like to modify the expression so that if there are parenthesis ( and ) , it should search between those parenthesis and then extract everything before the comma.

Is it possible to do something like this with just 1 expression? If so, how can I make it search within parenthesis if they exist?

score 2 · Accepted Answer · 2011-09-17 22:24:00Z

2

A conditional might help you here:

$stra = 'Naujasis Salemas, Šiaurės Dakota';
$strb = 'Jungtinės Valstijos (Centras, Šiaurės Dakota)';

$regex = '
  /^                    # Anchor at start of string.
    (?(?=.*\(.+,.*\))   # Condition to check for: presence of text in parenthesis.
        .*\(([^,]+)     # If condition matches, match inside parenthesis to first comma.
      | ([^,]+)         # Else match start of string to first comma.
    )
  /x
';
preg_match($regex, $stra, $matches) and print_r($matches);

/*
Array
(
    [0] => Naujasis Salemas
    [1] => 
    [2] => Naujasis Salemas
)
*/

preg_match($regex, $strb, $matches) and print_r($matches);

/*
Array
(
    [0] => Jungtinės Valstijos (Centras
    [1] => Centras
)
*/

Note that the index in $matches changes slightly above, but you might be able to work around that using named subpatterns.

edited Sep 17, 2011 at 22:24

answered Sep 17, 2011 at 13:19

user212218

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2 Comments

Arnaud Le Blanc Over a year ago

Nice :) (you could use the x modifier to comment in the regex directly ;) )

user212218 Over a year ago

Ah, thanks! I could've sworn I saw regex comments somewhere else on SO, and it was bugging me that I couldn't get it to work for mine (:

Arnaud Le Blanc · Accepted Answer · 2011-09-17 12:49:37Z

1

I think this one could do it:

[^-(]+(?=,)

This is the same regex as your, but it doesn't allow a parenthesis in the matched string. It will still match on the first subject, and on the second it will match just after the opening parenthesis.

Try it here: http://ideone.com/Crhzz

answered Sep 17, 2011 at 12:49

Arnaud Le Blanc

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Comments

Tim Pietzcker · Accepted Answer · 2011-09-17 12:50:30Z

1

You could use

[^(),]+(?=,)

That would match any text except commas or parentheses, followed by a comma.

answered Sep 17, 2011 at 12:50

Tim Pietzcker

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