SunshinePHP Developer Conference 2015

Operadores de Execução

O PHP suporta um operador de execução: acentos graves (``). Note que não são apóstrofes! O PHP tentará executar o conteúdo dos acentos graves como um comando do shell; a saída será retornada (isto é, ela não será simplesmente descarregada para a saída; ela pode ser atribuída a uma variável). A utilização do operador contra-apóstrofo é idêntica a função shell_exec().

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

Nota:

O operador de execução fica desabilitado quando safe mode está ativo ou shell_exec() está desabilitado.

Veja também a seção do manual sobre funções de execução de programas, popen() proc_open() e Utilizando o PHP em linha de comando.

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User Contributed Notes 8 notes

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22
robert
8 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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7
cs at kainaw dot com
8 years ago
After much trouble, I have concluded that the backtick operator (and shell_exec) have a limited buffer for the return.  My problem was that I was grepping a file with over 500,000 lines, receiving a response with well over 100,000 lines.  After a short pause, I was flooded with errors from grep about the pipe being closed.

I have searched, but I cannot find the exact size of the buffer used by the backtick operator and shell_exec.  So, to avoid this error, you must limit the output of your commands (such as using -m with grep).  Through trial and error, you can get the command to run without error.
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6
vdboor at codingdomain dot com
8 years ago
Note that most OS-es define two channels for file-output, the stdout and stderr (standard out and standard error). To read the data sent to stderr too, include 2>&1 in the backticks.
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2
reed-NO at SPAM-zerohour dot net
12 years ago
When a program is run using backticks, and the user cancels page loading (if your program is taking too long!), the shell running the program (the one in the backticks) may continue indefinitely on the server. I do not know if this is a bug, or just a danger of using this feature.  (It may depend on the way the browser "cancels" the request -- it was a problem on both IE and OmniWeb for the Mac).  Beware!
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1
aaron dot bentley at utoronto dot ca
11 years ago
waylanator's example can be dangerous, since it doesn't prevent characters with special meaning from being emitted to the commandline.  Programming errors or untrusted data could cause serious problems.  At the bare minimum, remove all non-alphanumeric characters before passing a string to the shell.  escapeshellarg() is also useful in *nix environments, but usually the best approach is to bypass the shell, using exec() etc.
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0
Anonymous
1 year ago
escapeshellarg()

if you're usimg popen, `` exec or anything else which takes a command-line
use escapeshellarg() on any variable parts, or risk being pwned.
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0
inform dot to dot kannan at gmail dot com
2 years ago
You can use the backtick operator on windows to run windows command too and it is not restricted only to execute the exe.
Example:
<?php
$output
= `dir`;
echo
"<pre>$output</pre>";
?>
It lists all the files in the directory
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0
waylanator no at spam hotmail dot com
11 years ago
In Windows it appears you can only call an executable file that resides in the system path which is defined by Windows.  As a workaround you can place a batch file in the system path that calls the program from it's dir. Just make sure to use short MS-DOS file and dir names.
For example:
If you were calling the file c:\program files\my program\program.exe do this:

mybat.bat look like this:
_________
@echo off
c:\progra~1\myprog~1\program.exe
_________

Save mybat.bat in c:\ or c:\windows or any other dir in the system path as defined by windows.

Then in php call the batch file:
_________
<?php
$test
= `c:\mybat.bat`;
echo
"<pre>$test</pre>";
?>
_________

That should do it.
Of course this will only work for a program you can run from the MS-DOS command prompt, but (as I understant it) that goes for any executable you call with PHP anyway.
Tested in Win98 running Apache 1.3.27 and PHP 4.3.0
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