题
I'm a PhP n00b. I'm reading some online tutorial, but I've already a question (a very basic question, I suppose):
I don't understand why the following code works properly:
https://stackoverflow.com/questions/20640943
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Russian<html>
<head>
<title> My Firts PHP page </title>
</head>
<body>
<?php
$userAgent = $_SERVER["HTTP_USER_AGENT"];
echo "<p>This is my awesome User Agent: <b>\"$userAgent\"</b></p>";
?>
</body>
</html>
and, instead, the following doesn't work although I protect the quotes inside the brackets:
<html>
<head>
<title> My Firts PHP page </title>
</head>
<body>
<?php
echo "<p>This is my awesome User Agent: <b>$_SERVER[\"HTTP_USER_AGENT\"]</b></p>";
?>
</body>
</html>
Thank you in advance.
解决方案
You've basically found an edge case of string interpolation. While alphanumeric array keys need to be quoted in PHP, in double-quoted strings they need to be unquoted:
echo "<p>This is my awesome User Agent: <b>$_SERVER[HTTP_USER_AGENT]</b></p>";
String parsing follows its own rules. In general, you can't drop random PHP code inside a string and get it executed.
其他提示
You could try one of these:
The curly bracket allows complex expressions within strings
<html>
<head>
<title> My Firts PHP page </title>
</head>
<body>
<?php
echo "<p>This is my awesome User Agent: <b>{$_SERVER[\"HTTP_USER_AGENT\"]}</b></p>";
?>
</body>
</html>
better yet, just use php for the piece you are outputting.
<html>
<head>
<title> My Firts PHP page </title>
</head>
<body>
<p>This is my awesome User Agent: <b><?php echo $_SERVER["HTTP_USER_AGENT"]; ?></b></p>
</body>
</html>
Wrong usage of escapinng quotes. See and test thhis:
echo "<p>This is my awesome User Agent: <b>". $_SERVER["HTTP_USER_AGENT"] ."</b></p>";
You can include a variable within the string like this:
echo "<p>This is my awesome User Agent: <b>{$_SERVER["HTTP_USER_AGENT"]}</b></p>";
It is nicer and cleaner if you used
echo "<p>This is my awesome User Agent: <b>". $_SERVER["HTTP_USER_AGENT"] ."</b></p>";
Or without single quotes in array key
echo "<p>This is my awesome User Agent: <b>$_SERVER[HTTP_USER_AGENT]</b></p>";
