shell_exec in PHP returns empty string

Question

shell_exec and exec are not returning any content. I can't figure out what's wrong.

Here's some code:

echo 'test: ';
$output = shell_exec('whoami');
var_export($output, TRUE);
echo PHP_EOL . '<br>' . PHP_EOL;

And here's the source of the output

test 2: 
<br>

I do not have control over the host, but I believe they're running SuPHP. According to phpinfo, safe_mode is off. Running whoami from SSH outputs the expected value.

I'm at a loss. Any idea how to debug this?

score 5 · Accepted Answer · answered Jul 10 '12 at 21:43

5

You're never printing the $output variable. The var_export() call returns the content of the variable when you call it with a true second parameter, it does not print it directly.

answered Jul 10 '12 at 21:43

lanzz

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I changed it to `echo var_export($output, TRUE);`. Now it outputs `NULL`. Any ideas? – sharoz Jul 10 '12 at 21:49
@sharoz Try `shell_exec('/usr/bin/whoami');` instead, and make sure /usr/bin is the correct path. – drew010 Jul 10 '12 at 21:50

score 0 · Answer 2 · answered Jul 10 '12 at 21:43

If you want the output from a shell command read back into PHP, you're probably going to need popen(). For example:

if( ($fp = popen("some shell command", "r")) ) {
    while( !feof($fp) ) {
        echo fread($fp, 1024);
        flush(); // input will be buffered
    }
    fclose($fp);
}

shell_exec in PHP returns empty string

2 Answers2