output

==================
image name:          centos:7.5.1804
/etc/redhat-release: CentOS Linux release 7.5.1804 (Core)
rpm --eval '%dist':  .el7
==================

==================
image name:          centos:7.4.1708
/etc/redhat-release: CentOS Linux release 7.4.1708 (Core)
rpm --eval '%dist':  .el7.centos
==================

==================
image name:          centos:7.3.1611
/etc/redhat-release: CentOS Linux release 7.3.1611 (Core)
rpm --eval '%dist':  .el7.centos
==================

==================
image name:          centos:7.2.1511
/etc/redhat-release: CentOS Linux release 7.2.1511 (Core)
rpm --eval '%dist':  .el7.centos
==================

==================
image name:          centos:7.1.1503
/etc/redhat-release: Derived from Red Hat Enterprise Linux 7.1 (Source)
rpm --eval '%dist':  .el7.centos
==================

==================
image name:          centos:7.0.1406
/etc/redhat-release: CentOS Linux release 7.0.1406 (Core)
rpm --eval '%dist':  .el7.centos
==================

verify-dist

#!/usr/bin/env bash

for image in centos:7.5.1804 centos:7.4.1708 centos:7.3.1611 centos:7.2.1511 centos:7.1.1503 centos:7.0.1406; do
    docker pull $image >/dev/null 2>/dev/null
    echo "=================="
    echo "image name:          $image"
    echo "/etc/redhat-release: $(docker run --rm "$image" cat /etc/redhat-release)"
    echo "rpm --eval '%dist':  $(docker run --rm "$image" rpm --eval '%{dist}')"
    echo "=================="
    echo
done