Question

For some strange reason this

echo system("echo 'echo hello > /dev/pts/2' | /usr/bin/at 19:36");

Refuses to work from my php script, however the command works fine when I just enter it through command line.

I know php has permission to execute some commands. I can run ‘ls’ from the php script but not the ‘at’ command. I’ve tried playing around with file permissions, but so far to no avail 🙁

edit

Permissions for /usr/bin/at are:

-rwxr-sr-x 1 daemon daemon 42752 Jan 15 2011 at

I think it’s a permissions problem, if I execute the php file from my ssh terminal it works fine, but not from the web.

Answer 1

What you are executing is

echo 'hello' > /dev/pts/2 | /usr/bin/at 19:36

meaning

echo 'hello' > /dev/pts/2

and pipe stdout to /usr/bin/at 19:36 but since you already redirected the echo to /dev/pts/2, this will be empty. What you probably meant to do is:

echo system("echo 'echo hello > /dev/pts/2' | /usr/bin/at 19:36");

You might also want to use shell_exec to pass the command through a shell or alternatively proc_open which gives you better control over stdin/out/err of the command you are executing. Your example would correspond to (adapted example from php.net docs):

<?php
$descriptorspec = array(
   0 => array("pipe", "r"),  // stdin is a pipe that the child will read from
   1 => array("pipe", "w"),  // stdout is a pipe that the child will write to
   2 => array("pipe", "w")  // stderr is a pipe that the child will write to
);

$process = proc_open('/usr/bin/at', $descriptorspec, $pipes);

if (is_resource($process)) {
    fwrite($pipes[0], 'echo "hello" > /dev/pts/2');
    fclose($pipes[0]);

    $stdout = stream_get_contents($pipes[1]);
    fclose($pipes[1]);

    $stderr = stream_get_contents($pipes[2]);
    fclose($pipes[2]);

    $return_value = proc_close($process);
    echo "command returned $return_value. stdout: $stdout, stderr: $stderr\n";
} else {
    echo "Process failed";
}
?>