escapeshellcmd
(PHP 4, PHP 5, PHP 7, PHP 8)
escapeshellcmd — Escape shell metacharacters
Description
$command): stringescapeshellcmd() escapes any characters in a string that might be used to trick a shell command into executing arbitrary commands. This function should be used to make sure that any data coming from user input is escaped before this data is passed to the exec() or system() functions, or to the backtick operator.
Following characters are preceded by a backslash:
&#;`|*?~<>^()[]{}$\, \x0A
and \xFF. ' and "
are escaped only if they are not paired. On Windows, all these characters
plus % and ! are preceded by a caret
(^).
Parameters
-
command -
The command that will be escaped.
Return Values
The escaped string.
Examples
Example #1 escapeshellcmd() example
<?php
// We allow arbitrary number of arguments intentionally here.
$command = './configure '.$_POST['configure_options'];
$escaped_command = escapeshellcmd($command);
system($escaped_command);
?>
escapeshellcmd() should be used on the whole command string, and it still allows the attacker to pass arbitrary number of arguments. For escaping a single argument escapeshellarg() should be used instead.
Spaces will not be escaped by escapeshellcmd()
which can be problematic on Windows with paths like:
C:\Program Files\ProgramName\program.exe.
This can be mitigated using the following code snippet:
<?php
$cmd = preg_replace('`(?<!^) `', '^ ', escapeshellcmd($cmd));
See Also
- escapeshellarg() - Escape a string to be used as a shell argument
- exec() - Execute an external program
- popen() - Opens process file pointer
- system() - Execute an external program and display the output
- backtick operator
