PHP - How to Know If Server Allows Shell_Exec

PHP - How to know if server allows shell_exec

First check that it's callable and then that it's not disabled:

is_callable('shell_exec') && false === stripos(ini_get('disable_functions'), 'shell_exec');

This general approach works for any built in function, so you can genericize it:

function isEnabled($func) {
    return is_callable($func) && false === stripos(ini_get('disable_functions'), $func);
}
if (isEnabled('shell_exec')) {
    shell_exec('echo "hello world"');
}

Note to use stripos, because PHP function names are case insensitive.

PHP exec - check if enabled or disabled

if(function_exists('exec')) {
    echo "exec is enabled";
}

shell_exec does not work on the server

The actual problem that persisted was the fact that there is a Linux Security module called SE-Linux(Security-Enhanced Linux) was enforced on my machine which provides a mechanism for supporting access control security policies, like MAC. It does not allow commands like shell_exec be executed by users other than the ones who have the permission to, like root user.

To get the the status of SE-Linux type in your shell sestatus or getenforced. It has 3 modes:

1) Enforcing: SE-Linux policy is enforced. SE-Linux denies access based on SE-Linux policy rules.

2)Permissive: SE-Linux policy is not enforced. SE-Linux does not deny access, but denials are logged for actions that would have been denied if running in enforcing mode.

3)Disabled: SE-Linux is disabled.

Hope this helps others, who might get stuck because of this.

shell_exec() and IF usage

It is only executed once. Specifically when you call the shell_exec function, NOT when you use the $cmd variable, which holds the results of the function.

Have a look at the documented return value of the function - http://php.net/manual/en/function.shell-exec.php

The output from the executed command

In other words, your code doesn't need the line $cmd; so could be rewritten like so:

$cmd = shell_exec("echo Hello!"); //command is fired here
if(strpos($cmd, 'Hello!') !== false) {
    // $cmd contains 'Hello!'
}

running shell_exec in php causes web server to hang

shell_exec — Execute command via shell and return the complete output as a string

shell_exec expects the file handle to be open, but you redirect everything to /dev/null and detach it.

As you plan to detach the process and remove all the output, you should use exec() and escapeshellcmd()

see: http://www.php.net/manual/en/function.exec.php

How to check if a shell command exists from PHP

On Linux/Mac OS Try this:

function command_exist($cmd) {
    $return = shell_exec(sprintf("which %s", escapeshellarg($cmd)));
    return !empty($return);
}

Then use it in code:

if (!command_exist('makemiracle')) {
    print 'no miracles';
} else {
    shell_exec('makemiracle');
}

Update:
As suggested by @camilo-martin you could simply use:

if (`which makemiracle`) {
    shell_exec('makemiracle');
}

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