Regular expression with PHP to replace newlines

Question

I am trying to replace all the \n in a json string with a double pipe ||. Here is an example of a string :

{"comment":"test1
test2
test3"}';

Here is the regex I have done :

preg_match('/"comment":"(([^\n\t\r"]*)([\n\t\r]*))+"/', $a, $t);

The result of this preg_match is

Array
(
    [0] => "comment":"test1
test2
test3"
    [1] => 
    [2] => 
    [3] => 
)

I can't find what is wrong with my regexp.

Do I need a recursive pattern (?R) ?

Thanks.

if you want to replace \n chars then why you use preg_match ? — Avinash Raj
– Avinash Raj, Commented Nov 26, 2014 at 11:42
Actually I don't want to replace all the newlines but only newlines in the comment. If you have a || just after {, the php function json_decode will encounter a problem. — Mahcih
– Mahcih, Commented Nov 26, 2014 at 11:47
@Hicham: cf my answer: decode the string, change the comment value, and encode the data again. It's the easiest and safest way to go — Elias Van Ootegem
– Elias Van Ootegem, Commented Nov 26, 2014 at 11:48

Avinash Raj · Accepted Answer · 2014-11-26 12:30:53Z

1

Use preg_replace function like below. I assumed that your input have balanced paranthesis.

preg_replace('~(?:"comment"[^\n]*|\G)\K\n([^{}\n]*)~', '||\1', $str)

DEMO

edited Nov 26, 2014 at 12:30

answered Nov 26, 2014 at 11:46

Avinash Raj

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8 Comments

Mahcih Over a year ago

what does [^{}] represent ? Every caracter which is not { or } ?

Avinash Raj Over a year ago

yep, match all the chars except { or }

Mahcih Over a year ago

And if I want to replace it only in the content of the comment "comment":"HERE" I tried \n(?="comment":".*")

Avinash Raj Over a year ago

What's your expected output?

Mahcih Over a year ago

foo {"comment": "test1||test2||test3"}'; bar

|

vks · Accepted Answer · 2014-11-26 12:04:30Z

0

\n+(?=[^{]*})

You can simply use this.Replace with ||.

$re = "/\\n+(?=[^{]*})/i";
$str = "{\"comment\":\"test1\n test2\n test3\"}'";
$subst = "||";

$result = preg_replace($re, $subst, $str);

edited Nov 26, 2014 at 12:04

answered Nov 26, 2014 at 11:42

vks

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2 Comments

Mahcih Over a year ago

Actually I don't want to replace all the newlines but only newlines in the comment. If you have a || just after {, the php function json_decode will encounter a problem.

Henrik Over a year ago

@Hicham A newline is not allowed in a json value, they should all be replaced with \n. Then you can use json_decode() as said in the missing answer.

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