Building up on @Poikilos's answer:

eval "$(
  php -r '
    require("input.php");
    foreach(get_defined_vars() as $name => $var)
      if (is_string($var))
        echo "php_", $name, "=", escapeshellarg($var), "\n";
  '
)"

Would create a $php_varname shell variable for each $varname string PHP variable.

Beware that PHP variables that contain NUL bytes trip escapeshellargs().

Building up on @Poikilos's answer:

eval "$(
  php -r '
    require("config.php");
    foreach(get_defined_vars() as $name => $var)
      if (is_string($var))
        echo "php_", $name, "=", escapeshellarg($var), "\n";
  '
)"

Would define a $php_varname shell variable for each $varname string PHP variable.

Beware that PHP variables that contain NUL bytes trip escapeshellargs().