docekrfile遇到问题，这些红色+号啥意思，为什么会这样？

Question

这些红色+号啥意思啊？

源dockerfile在下面：

FROM alpine:latest

LABEL maintainer="[e-mail]"

ENV JAVA_VERSION_MAJOR=8
JAVA_VERSION_MINOR=231
JAVA_VERSION_BUILD=11
JAVA_PACKAGE=jdk
JAVA_JCE=standard
JAVA_HOME=/opt/jdk
PATH=${PATH}:/opt/jdk/bin
GLIBC_REPO=https://github.com/sgerrand/alpine-pkg-glibc
GLIBC_VERSION=2.30-r0
LANG=C.UTF-8

RUN set -ex &&
[[ ${JAVA_VERSION_MAJOR} != 7 ]] || ( echo >&2 'Oracle no longer publishes JAVA7 packages' && exit1 ) &&
apk -U upgrade &&
apk add libstdc++ curl ca-certificates bash tzdata &&
ln -sf /usr/share/zoneinfo/Asia/Shanghai /etc/localtime &&
echo "Asia/Shanghai" > /etc/timezone &&
for pkg in glibc-${GLIBC_VERSION} glibc-bin-${GLIBC_VERSION} glibc-i18n-${GLIBC_VERSION}; do curl -sSL ${GLIBC_REPO}/releases/download/${GLIBC_VERSION}/${pkg}.apk -o /tmp/${pkg}.apk; done &&
apk add --allow-untrusted /tmp/.apk &&
rm -v /tmp/.apk &&
( /usr/glibc-compat/bin/localedef --force --inputfile POSIX --charmap UTF-8 C.UTF-8 || true ) &&
echo "export LANG=C.UTF-8" > /etc/profile.d/locale.sh &&
/usr/glibc-compat/sbin/ldconfig /lib /usr/glibc-compat/lib &&
mkdir -p /opt &&
curl -sSL -o /tmp/java.tar.gz \http://download.macromedia.com/pub/coldfusion/java/java8/JDK$%7BJAVA_VERSION_MAJOR%7Du$%7BJAVA_VERSION_MINOR%7D/$%7BJAVA_PACKAGE%7D-$%7BJAVA_VERSION_MAJOR%7Du$%7BJAVA_VERSION_MINOR%7D-linux-x64.tar.gz &&
JAVA_PACKAGE_SHA256=$(curl -sSL https://www.oracle.com/webfolder/s/digest/${JAVA_VERSION_MAJOR}u${JAVA_VERSION_MINOR}checksum.html | grep -E "${JAVA_PACKAGE}-${JAVA_VERSION_MAJOR}u${JAVA_VERSION_MINOR}-linux-x64.tar.gz" | grep -Eo '(sha256: )[^<]+' | cut -d: -f2 | xargs) && \echo "${JAVA_PACKAGE_SHA256} /tmp/java.tar.gz" > /tmp/java.tar.gz.sha256 &&
sha256sum -c /tmp/java.tar.gz.sha256 &&
gunzip /tmp/java.tar.gz &&
tar -C /opt -xf /tmp/java.tar &&
ln -s /opt/jdk1.${JAVA_VERSION_MAJOR}.0_${JAVA_VERSION_MINOR} /opt/jdk &&
if [ "${JAVA_JCE}" == "unlimited" ]; then echo "Installing Unlimited JCE policy" >&2 &&
curl -jksSLH "Cookie: oraclelicense=accept-securebackup-cookie" -o /tmp/jce_policy-${JAVA_VERSION_MAJOR}.zip \http://download.oracle.com/otn-pub/java/jce/$%7BJAVA_VERSION_MAJOR%7D/jce_policy-$%7BJAVA_VERSION_MAJOR%7D.zip &&
cd /tmp && unzip /tmp/jce_policy-${JAVA_VERSION_MAJOR}.zip &&
cp -v /tmp/UnlimitedJCEPolicyJDK8/*.jar /opt/jdk/jre/lib/security;
fi &&
sed -i s/#networkaddress.cache.ttl=-1/networkaddress.cache.ttl=10/$JAVA_HOME/jre/lib/security/java.security &&
apk del curl glibc-i18n &&
echo 'hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4' >> /etc/nsswitch.conf

Answer 1

+ 号不是很明显吗。。。就是你编写的dockerfile文件要执行的命令啊，
这样说吧，因为docker 镜像是分层的（可以去看看docker镜像的分层原理），没执行一样东西，就会添加一层，你可以理解为 + 号，就是执行了一样东西，增加了一层。也是一种记忆方式。