PHP exec returns correctly for some commands using sudo, not others

Question

I'm getting successful output when I issue the following in a PHP script:

$peers_summary = exec('sudo asterisk -x "sip show peers"', $sip_peers);

$sip_peers contains the full output of the exec command, listing the peers in standard table format that Asterisk provides. However, when I issue:

$test = exec('sudo asterisk -x "sip show peer trunk-to-pbx"', $trunk);

$trunk is completely empty: array(0) {} , and $test is an empty string: string(0) ""

trunk-to-pbx is a valid peer in my Asterisk installation, and I've verified that issuing sudo asterisk -x "sip show peer trunk-to-pbx" at the prompt is successful (as is sudo asterisk -x "sip show peers" ), so I'm not sure why the second command returns empty from exec() . I thought initially that it might be an output character limit, but the output has less than 2,000 characters - couldn't be a memory or limit issue. I tried set_time_limit(0) even though the execution is virtually instantaneous at the prompt.

Why is the second exec() returning empty?

Answer 1

The problem was not with exec() , or asterisk , or the command I was passing to exec() ; there's a sudoers file that whitelists commands, and my command needed inclusion before the exec() would work. Inherited codebase. Thanks Chris Stryczynski , for your suggestions.