\\n vs. PHP_EOL vs. ?

问题:

In most cases, as for one interactive website, when we output multiple lines of contents to web client browser, in my opinion, <BR /> is much more preferable than other two: \n or PHP_EOL.

Else, we need to use "<pre></pre>" to wrap the output content or use nl2br() to insert <BR /> before \n so as the multiple line mark can take effect in HTML. Like following example.

$fruits = array('a'=>'apple', 'b'=>'banana', 'c'=>'cranberry');

// Multiple lines by \n
foreach( $fruits as $key => $value ){
    echo "$key => $value \n" ;
}

// Multiple lines by PHP_EOL
reset( $fruits );
while ( list($key, $value) = each( $fruits ) ){
    echo ("$key => $value" . PHP_EOL);
}

// Multiple lines by <BR />
reset( $fruits );
while ( list($key, $value) = each( $fruits ) ){
    echo ("$key => $value <BR />");
}

Some people believe PHP_EOL is useful when writing data to a file, example a log file. It will create line breaks no matter whatever your platform.

Then, my question is when we use \n? What's the difference between \n and PHP_EOL, and <BR />? Could any body have a big list of each of their pros and cons?

回答1:

DOS, Unix, and Mac (pre-OS X and OS X) all use different characters or character combinations to represent "go to the next line."

• DOS - Uses a CR+LF (that's ASCII 13 followed by an ASCII 10, or \r\n) to represent a new line.

• Unix - Uses an LF (that's ASCII 10, or \n) to represent a new line.

• Mac (pre-OS X) - Uses a CR (that's ASCII 13, or \r) to represent a new line.

• Mac (OS X) - Like Unix, uses an LF to represent a new line.

Therefore, when to use each one depends on what you're going for. If you're writing for a specific platform without the intention of portability, use the character or character combination to break lines that matter to that platform. The purpose of PHP_EOL is to automatically choose the correct character for the platform, so that your new lines are platform-independent.

All of these appear as a single space within a browser as browsers collapse whitespace into a display space for display purposes (unless you're using <pre> as you mentioned, or CSS that changes the behavior of whitespace). This is where <br> comes in, as you've mentioned, which will convert these \n new line characters into <br> so that they provide line breaks in HTML display.

回答2:

<br>

<br> is only to be used when dividing up text. You may see this used for spacing out elements within an html document, but that is not its purpose, as layout spacing should be achieved with CSS such as margin. Here's a decent use case:

<p>This <br> is <br> some <br> text.</p>

I typically break up my text with linebreaks for readability, so I wouldn't want the linebreaks rendered in the document. That being, the <br> tag is necessary.

CSS whitespace, <pre>

The html element <pre> is an element that, by default, uses CSS rule white-space: pre; so that the document's whitespace is rendered within that element. Normally, only a single space would be rendered regardless of the amount of whitespace in the document. A very good use of this style is for code blocks. If I write a code block, I will naturally space it as I intend and don't particularly care to wrap a <p> tag around each line (that's not semantic anyway) and I don't want to litter my code with <br> either. Even worse, there's the code indentation! whitespace: pre makes a lot of sense here.

<pre>
function foo() {
  //etc
}
</pre>

\r, \n, PHP_EOL

Depending on the platform your php code is running from, you'll need to render a linebreak with \r, \n\, or both \r\n. PHP_EOL will automatically choose for you, so it is the most dynamic approach.

回答3:

It makes no sense to compare a HTML linebreak <br> with actual text linebreaks. <br> is only a linepage in the browser's rendering of a website whereas \n and PHP_EOL are actual, source code linebreaks.

As you mention yourself, PHP_EOL will work regardless of platform and is therefore also preferred over \n. Initially, \n was only the standard linebreak on UNIX, whereas Macintosh used \r and Windows/DOS used a combination of the two: \r\n. When using PHP_EOL, however, you don't have to worry about platform at all.

Nowadays, most systems and editors are tolerant enough to accept whatever linebreak you decide to use, but using the correct one is obviously preferred and most-easily achieved with PHP_EOL, so there's really no reason not to use it.

回答4:

I have to run scripts on cron and save results to a log file. But sometimes I run the script on my browser. So I do the following test in order to use the correct end of line char:

<?php
$eol = (isset($_SERVER['SHELL'])) ? PHP_EOL : "<br />";
echo "DISCOVER". $eol;
?>

回答5:

You can create a function with Flavio's code, that always sets the correct newline, no matter if you run it on the shell or in the browser:

<?php
function nl($string) {
  if(isset($_SERVER['SHELL'])) return preg_replace('/\<br(\s*)?\/?\>/i', PHP_EOL, $string);
  return nl2br($string);
}


print nl("One\nTwo<br>Three\r\nFour<br />Five
Six" . PHP_EOL);
?>