执行运算符

PHP 支持一个执行运算符:反引号(``)。注意这不是单引号!PHP 将尝试将反引号中的内容作为 shell 命令来执行,并将其输出信息返回(即,可以赋给一个变量而不是简单地丢弃到标准输出)。使用反引号运算符"`"的效果与函数 shell_exec() 相同。

<?php
$output 
= `ls -al`;
echo 
"<pre>$output</pre>";
?>

Note:

关闭了 shell_exec() 时反引号运算符是无效的。

Note:

与其它某些语言不同,反引号不能在双引号字符串中使用。

User Contributed Notes

ohcc at 163 dot com 04-Dec-2016 02:22
You can use variables within a pair of backticks (``).

<?php
    $host
= 'www.wuxiancheng.cn';
    echo `
ping -n 3 {$host}`;
?>
robert 01-Mar-2006 11:25
Just a general usage note.  I had a very difficult time solving a problem with my script, when I accidentally put one of these backticks at the beginning of a line, like so:

[lots of code]
`    $URL = "blah...";
[more code]

Since the backtick is right above the tab key, I probably just fat-fingered it while indenting the code.

What made this so hard to find, was that PHP reported a parse error about 50 or so lines *below* the line containing the backtick.  (There were no other backticks anywhere in my code.)  And the error message was rather cryptic:

Parse error: parse error, expecting `T_STRING' or `T_VARIABLE' or `T_NUM_STRING' in /blah.php on line 446

Just something to file away in case you're pulling your hair out trying to find an error that "isn't there."