PHP - How to Get Shell Errors Echoed Out to Screen

PHP - How to get Shell errors echoed out to screen

The error data is output from the target program's STDERR stream. You can get access to the error data through the normal returned string from shell_exec() by appending 2>&1 to the command, which will redirect STDERR to STDOUT, the stream that you are currently seeing:

var_dump(shell_exec("ffmpeg -i /var/www/html/sitedomain/httpdocs/tmp/ebev1177.mp4 2>&1"));

You may also want to take a look at proc_open() which will allow you to get access to STDIN, STDOUT and STDERR as three individual streams, which can afford much finer grained control over the target program and exactly how you handle the input and output to it, including redirecting any and all of them directly to a log file if so desired. Be aware though that this is a much more complex mechanism with many pitfalls and tripping hazards.

More information on the standard streams can be found here.

php run command line and pipe std err to variable

ok I was able to find a solution. You need to set up a native process to configure the pipes.

$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 file to write to
);
$cwd = '/tmp';
$env = array('some_option' => 'aeiou');

$process = proc_open('ls -lasdfsdfwefwekj', $descriptorspec, $pipes, $cwd, $env);

/*fwrite($pipes[0], '<?php print_r($_ENV); ?>');
*/
fclose($pipes[0]);

echo "stdout=".stream_get_contents($pipes[1]);
echo "stderr=".stream_get_contents($pipes[2]);

fclose($pipes[1]);
fclose($pipes[2]);

$return_value = proc_close($process);

echo "command returned $return_value\n";

php shell_exec command doesn't give an outpu of the python scriptt in ubuntu

1. Try to catch error stream by appending 2>&1 to the command: $output = shell_exec("python3 $chk $sym 2>&1"); See PHP - How to get Shell errors echoed out to screen

2. You potentially have an OS command injection vulnerability (you concatenate user input with a shell command). See https://portswigger.net/web-security/os-command-injection

Shell output not being fully retrieved by PHP!

You read only the first 4,096 bytes from the pipe, you'll need to place the fread/print_r in a loop and check for the end-of-file using the feof function.

$handle = popen('python last', 'r');

while(!feof($handle))
{
    print_r(fread($handle, 4096));
} 

pclose($handle);

Can I try/catch a warning?

Set and restore error handler

One possibility is to set your own error handler before the call and restore the previous error handler later with restore_error_handler().

set_error_handler(function() { /* ignore errors */ });
dns_get_record();
restore_error_handler();

You could build on this idea and write a re-usable error handler that logs the errors for you.

set_error_handler([$logger, 'onSilencedError']);
dns_get_record();
restore_error_handler();

Turning errors into exceptions

You can use set_error_handler() and the ErrorException class to turn all php errors into exceptions.

set_error_handler(function($errno, $errstr, $errfile, $errline) {
    // error was suppressed with the @-operator
    if (0 === error_reporting()) {
        return false;
    }
    
    throw new ErrorException($errstr, 0, $errno, $errfile, $errline);
});

try {
    dns_get_record();
} catch (ErrorException $e) {
    // ...
}

The important thing to note when using your own error handler is that it will bypass the error_reporting setting and pass all errors (notices, warnings, etc.) to your error handler. You can set a second argument on set_error_handler() to define which error types you want to receive, or access the current setting using ... = error_reporting() inside the error handler.

Suppressing the warning

Another possibility is to suppress the call with the @ operator and check the return value of dns_get_record() afterwards. But I'd advise against this as errors/warnings are triggered to be handled, not to be suppressed.

PHP shell_exec() - not printing dynamic output, only prints static echo text

Is wanpipemon in the path of whatever shell PHP's using to execute the script? The 'file not found' type errors would be written to stderr and not trapped by your string building in the script, and also not caught by PHP unless you did stderr redirection:

$output = shell_exec('/usr/sbin/linesta.sh 2>&1');
                                           ^^^^--- redirect stderr to stdout.

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