Execution Operators

PHP supports one execution operator: backticks (``). Note that these are not single-quotes! PHP will attempt to execute the contents of the backticks as a shell command; the output will be returned (i.e., it won't simply be dumped to output; it can be assigned to a variable). Use of the backtick operator is identical to shell_exec().

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

Notă:

The backtick operator is disabled when modul securizat is enabled or shell_exec() is disabled.

Notă:

Unlike some other languages, backticks have no special meaning within double-quoted strings.

See also the manual section on Program Execution functions, popen() proc_open(), and Using PHP from the commandline.

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User Contributed Notes 2 notes

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103
robert
13 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."
up
46
ohcc at 163 dot com
2 years ago
You can use variables within a pair of backticks (``).

<?php
    $host
= 'www.wuxiancheng.cn';
    echo `
ping -n 3 {$host}`;
?>
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