Replace multiple new lines with a single newline

How do I replace multiple consecutive newlines with one newline. There could be up to 20 newlines next 开发者_StackOverflow中文版to each other. For example

James said hello\n\n\n\n Test\n Test two\n\n

Should end up as:

James said hello\n Test\n Test two\n

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Try this one:

$str = "Hello\n\n\n\n\nWorld\n\n\nHow\nAre\n\nYou?";
$str = preg_replace("/\n+/", "\n", $str);
print($str);

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Improving on Marc B's answer:

$fixed_text  = preg_replace("\n(\s*\n)+", "\n", $text_to_fix);

Which should match an initial newline, then at least one of a group of any amount of whitespace followed by a newline and replace it all with a single newline.

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$fixed_text = preg_replace("\n+", "\n", $text_to_fix);

This should do it, assuming that the consecutive newlines are truly consecutive and don't have any whitespace (tabs, spaces, carriage returns, etc...) between them.

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$str = 'James said hello\n\n\n\n Test\n Test two\n\n';
echo preg_replace('{(\\\n)\1+}','$1',$str);

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In regex:

• + means "one or more of the previous expression"
• {2,} means "two or more of the previous expression"

For the requirements in this question, there is no point replacing a single \n with a single \n because nothing changes for that substring. In other words, /\n+/ is simply doing more work than necessary.

It makes much more sense to use a ranged quantifier of two or more.

Code: (Demo)

$string = "James said hello\n\n\n\n Test\n Test two\n\n";
echo json_encode(
    preg_replace("/\n{2,}/", "\n", $string)
);

Output:

"James said hello\n Test\n Test two\n"

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In other situations, it may be advantageous to replace newline sequences that may be from different operating systems with \R. This metacharacter matches \r\n or \n. Here is a modified pattern which will replace two or more newline sequences with the server's designated newline character sequence:

$string = "James\r\n said\n\r\n hello\r\n\r\n\r\n Test\n Test two\n\n";
echo json_encode(
    preg_replace("/\R{2,}/", PHP_EOL, $string)
);
// "James\r\n said\n hello\n Test\n Test two\n"
//       ^^^^----treated as one newline character sequence