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单引号和双引号的区别

双引号解析变量

单引号不解析变量

单引号效率较高

$username = 'king';
echo '$username';//$username
echo "<hr/>";
echo "$username";//king

内容和界定符冲突时使用转义符

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双引号解析所有的转义符

$str = 'this is a test';
//$str='this is a test of king's PHP';//单引号需要转义
$str = 'this is a test of king\'s PHP';//this is a test of king's PHP
echo $str;
echo "<br/>";
$str = "He said \"I'm Fine\" Thank you!";
echo $str;//He said "I'm Fine" Thank you!

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echo "1\n2\r3\t4\$5\\678";
//1 2 3 4$5\678

查看源代码

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单引号只转义反斜线和单引号

echo '1\n2\r3\t4\$5\\6\'78';
//1\n2\r3\t4\$5\6'78

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