composer require tm/gpg-verifier ^1.0

use TM\GPG\Verification\Verifier;

$verifier = new Verifier;
$verifier->verify('my-file.sig', 'my-file');

use TM\GPG\Verification\Verifier;
use TM\GPG\Verification\Exception\FailedVerificationException;
use TM\GPG\Verification\Exception\ExecutableException;
use TM\GPG\Verification\Exception\NotExistException;

$verifier = new Verifier('/path/to/gpg');

try {
    $verifier->verify('my-file.sig', 'my-file');
} catch(FailedVerificationException $exception) {
    // verification failed
} catch(NotExistException $exception) {
    // missing signature- or source-file
} catch(ExecutableException $exception) {
    // something with the executable is wrong
}