Answers for "run composer in different php version'"

composer use different php version

/usr/bin/php7.1 /usr/local/bin/composer update

run composer with specific php version

#/usr/bin/php7.1 /usr/local/bin/composer update
#or edit your composer.json file and specify the version you want
"config": {
    "platform": {
        "php": "7.1.3"
    }
}