example.php

<?php 

include __DIR__ . '/Shell.php';

// List entries
$command = Shell::exec("ls -l");
if ($command->failed()) {
  echo "Failed to list entries!\n";
  exit(__LINE__); // exit script with error code (non-zero), using line number might make debuggin easier
}
else {
  echo "Entries: \n" . $command->output;
}

Shell.php

<?php

class Shell {

  public $command;
  public $output_array;
  public $output;
  public $exit_code;

  public function __construct($command, $exit_code, array $output_array) {
    $this->command = $command;
    $this->exit_code = $exit_code;
    $this->output = implode("\n", $output_array);
    $this->output_array = $output_array;
  }

  /**
   * Run command and capture output and exit  code
   *
   * @param string $command
   *  Shell command to execute
   * @param bool $capture_errors
   *  Set this to TRUE to include errors in output string
   *
   * @return static
   */
  public static function exec($command, $capture_errors = TRUE) {
    ob_start();
    $output_array = array();
    exec($command . ($capture_errors ? ' 2>&1' : ''), $output_array, $exit_code);
    ob_end_clean();
    return new static($command, $exit_code, $output_array);
  }

  /**
   * Returns TRUE if command failed with a non-zero exit code
   *
   * @return bool
   */
  public function failed() {
    return $this->exit_code != 0;
  }

}