PHP Velho Oeste 2024

実行演算子

PHP は 1 種類の実行演算子、バッククォート (``) をサポートします。 シングルクォートではないことに注意してください! PHP は、バッククォートの 中身をシェルコマンドとして実行しようとします。出力が返されます (すなわち、出力を単にダンプするのではなく、変数に代入することが できます) 。 バッククォート演算子の使用は shell_exec() と等価です。

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

注意:

バッククォート演算子は、 shell_exec() が無効な場合は無効となります。

注意:

他の言語とは異なり、 ダブルクォートで囲まれた文字列の中でのバッククォート演算子には何の効力もありません。

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User Contributed Notes 3 notes

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152
robert
17 years ago
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."
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110
ohcc at 163 dot com
7 years ago
You can use variables within a pair of backticks (``).

<?php
$host
= 'www.wuxiancheng.cn';
echo `
ping -n 3 {$host}`;
?>
up
2
paolo.bertani
1 year ago
If you want to avoid situations like the one described by @robert you may want to disable `shell_exec` and -as a consequence- the backtick operator.

To do this just edit the `php.ini` file and add `shell_exec` to the `disable_functions` setting:

; This directive allows you to disable certain functions.
; It receives a comma-delimited list of function names.
; https://php.net/disable-functions
disable_functions = "shell_exec"

Then you can still use `exec()` to run terminal commands.
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