php单引号和双引号

Question

//remove line breaks
function safeEmail($string) {
     return  preg_replace( '((?:
||\t|%0A|%0D|%08|%09)+)i' , '', $string );
}

/*** example usage 1***/
$from = 'HTML Email\t
';

/*** example usage 2***/
$from = "HTML Email\t
";

if(strlen($from) < 100)
{
    $from = safeEmail($from);

    echo $from;
}

1 returns HTML Email\t while 2 returns HTML Email

what's with the quotes?

Answer 1

As per the PHP Documentation

Unlike the double-quoted and heredoc syntaxes, variables and escape sequences for special characters will not be expanded when they occur in single quoted strings.

In other words, double quoted strings expand variables and escape sequences for special characters. Single quoted strings don't.

So in example1, with the single quoted string, the string is exactly as you see it. Slashes and all.

But in example2, rather than ending with the string \t , it ends with a carriage return, a tab and then a new line. In other words the escape sequences for special characters are expanded.