Regex with multiple newlines in sequence

Question

I'm trying to use PHP's split() (preg_split() is also an option if your answer works with it) to split up a string on 2 or more \r\n's. My current effort is:

split("(\r\n){2,}",$nb);

The problem with this is it matches every time there is 2 or 3 \r\n's, then goes on and finds the next one. This is ineffective with 4 or more \r\n's.

I need all instances of two or more \r\n's to be treated the same as two \r\n's. For example, I'd need

Hello\r\n\r\nMy\r\n\r\n\r\n\r\n\r\n\r\nName is\r\nShadow

to become

array('Hello','My','Name is\r\nShadow');

Tomalak · Accepted Answer · 2009-06-23 19:49:50Z

3

preg_split() should do it with

$pattern = "/(\\r\\n){2,}/";

answered Jun 23, 2009 at 19:49

Tomalak

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3 Comments

chendral Over a year ago

yes, because pcre works "greedy" by default i.e. {2,} tries to match as many characters as possible while split() will stop the pattern matching as soon as it's fulfilled.

Alex S Over a year ago

It didn't do it with just that, but I found the PREG_SPLIT_NO_EMPTY flag which accomplishes the same thing for my purposes.

Tomalak Over a year ago

@chendral: Hm... @Gumbo's answer seems to indicate otherwise.

merkuro · Accepted Answer · 2009-06-23 19:54:41Z

1

What about the following suggestion:

$nb = implode("\r\n", array_filter(explode("\r\n", $nb)));

answered Jun 23, 2009 at 19:54

merkuro

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Comments

Gumbo · Accepted Answer · 2009-06-23 19:55:20Z

1

It works for me:

$nb = "Hello\r\n\r\nMy\r\n\r\n\r\n\r\n\r\n\r\nName is\r\nShadow";
$parts = split("(\r\n){2,}",$nb);
var_dump($parts);
var_dump($parts === array('Hello','My',"Name is\r\nShadow"));

Prints:

array(3) {
  [0]=>
  string(5) "Hello"
  [1]=>
  string(2) "My"
  [2]=>
  string(15) "Name is
Shadow"
}
bool(true)

Note the double quotes in the second test to get the characters represented by \r\n.

answered Jun 23, 2009 at 19:55

Gumbo

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Comments

Alex S · Accepted Answer · 2009-06-23 20:01:27Z

0

Adding the PREG_SPLIT_NO_EMPTY flag to preg_replace() with Tomalak's pattern of "/(\\r\\n){2,}/" accomplished this for me.

answered Jun 23, 2009 at 20:01

Alex S

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Comments

mickmackusa · Accepted Answer · 2021-03-30 22:05:48Z

0

\R is shorthand for matching newline sequences across different operating systems. You can prevent empty elements being created at the start and end of your output array by using the PREG_SPLIT_NO_EMPTY flag or you could call trim() on the string before splitting.

Code: (Demo)

$string = "\r\n\r\nHello\r\n\r\nMy\r\n\r\n\r\n\r\n\r\n\r\nName is\r\nShadow\r\n\r\n\r\n\r\n";

var_export(preg_split('~\R{2,}~', $string, 0, PREG_SPLIT_NO_EMPTY));

echo "\n---\n";

var_export(preg_split('~\R{2,}~', trim($string)));

Output from either technique:

array (
  0 => 'Hello',
  1 => 'My',
  2 => 'Name is
Shadow',
)

answered Mar 30, 2021 at 22:05

mickmackusa♦

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