try this:

```bash
php -d memory_limit=2048M ~/.phpenv/versions/$(phpenv version-name)/bin/composer update
```

btw, a simpler solution than updating the memory limit everywhere when calling PHP (for composer and then for behat) would be to change the PHP config instead:

```bash
echo "memory_limit=4096M" >> sylius.ini
phpenv config-add sylius.ini
```