Create command to return the value of an env var for current env

module/CLI/src/Command/Config/ReadEnvVarCommand.php

@@ -0,0 +1,58 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Shlinkio\Shlink\CLI\Command\Config;
+
+use Shlinkio\Shlink\CLI\Util\ExitCode;
+use Shlinkio\Shlink\Core\Config\EnvVars;
+use Symfony\Component\Console\Command\Command;
+use Symfony\Component\Console\Exception\InvalidArgumentException;
+use Symfony\Component\Console\Input\InputArgument;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Output\OutputInterface;
+use Symfony\Component\Console\Style\SymfonyStyle;
+
+use function Shlinkio\Shlink\Config\formatEnvVarValue;
+use function Shlinkio\Shlink\Core\ArrayUtils\contains;
+use function Shlinkio\Shlink\Core\enumValues;
+use function sprintf;
+
+class ReadEnvVarCommand extends Command
+{
+    public const NAME = 'env-var:read';
+
+    protected function configure(): void
+    {
+        $this
+            ->setName(self::NAME)
+            ->setHidden()
+            ->setDescription('Display current value for an env var')
+            ->addArgument('envVar', InputArgument::REQUIRED, 'The env var to read');
+    }
+
+    protected function interact(InputInterface $input, OutputInterface $output): void
+    {
+        $io = new SymfonyStyle($input, $output);
+        $envVar = $input->getArgument('envVar');
+        $validEnvVars = enumValues(EnvVars::class);
+
+        if ($envVar === null) {
+            $envVar = $io->choice('Select the env var to read', $validEnvVars);
+        }
+
+        if (! contains($envVar, $validEnvVars)) {
+            throw new InvalidArgumentException(sprintf('%s is not a valid Shlink environment variable', $envVar));
+        }
+
+        $input->setArgument('envVar', $envVar);
+    }
+
+    protected function execute(InputInterface $input, OutputInterface $output): int
+    {
+        $envVar = $input->getArgument('envVar');
+        $output->writeln(formatEnvVarValue(EnvVars::from($envVar)->loadFromEnv()));
+
+        return ExitCode::EXIT_SUCCESS;
+    }
+}