maven的命令程序mvn脚本分析

最近公司将svn迁移到git，而且使用maven管理代码仓库，所以小小的研究了一下，为自动化持续集成做知识准备，以下是分析了maven的命令程序mvn:
总体感觉与tomcat的启动脚本startup大同小异

#!/bin/sh
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# to you under the Apache License, Version 2.0 (the
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#
#    http://www.apache.org/licenses/LICENSE-2.0 #
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# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
# KIND, either express or implied.  See the License for the
# specific language governing permissions and limitations
# under the License.
# ----------------------------------------------------------------------------
# ----------------------------------------------------------------------------
# Maven2 Start Up Batch script
#
# Required ENV vars:
# ------------------
#   JAVA_HOME - location of a JDK home dir
#
# Optional ENV vars
# -----------------
#   M2_HOME - location of maven2's installed home dir
#   MAVEN_OPTS - parameters passed to the Java VM when running Maven
#     e.g. to debug Maven itself, use
#       set MAVEN_OPTS=-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=8000
#   MAVEN_SKIP_RC - flag to disable loading of mavenrc files
# ----------------------------------------------------------------------------
#如果系统里有多JDK版本，就可以在这里指定JAVA_HOME，这样即使JAVA_HOME环境变量不是这个，也可以从这里弥补
#M2_HOME 也可以在这里指定，maven会在家目录生成.m2目录
#MAVEN_OPTS 这个是设maven启动参数的，有兴趣的同学可以研究下
JAVA_HOME=/usr/java/jdk1.6.0_38
if [ -z "$MAVEN_SKIP_RC" ] ; then
if [ -f /etc/mavenrc ] ; then
. /etc/mavenrc
fi
if [ -f "$HOME/.mavenrc" ] ; then
. "$HOME/.mavenrc"
fi
fi
#如果环境变量MAVEN_SKIP_RC存在，则从下面3个外部文件找是否设置maven的环境变量，
#下面是系统环境检查，和tomcat的startup.sh一曲同工
# OS specific support.  $var _must_ be set to either true or false.
cygwin=false;
darwin=false;
mingw=false
case "`uname`" in
CYGWIN*) cygwin=true ;;
MINGW*) mingw=true;;
Darwin*) darwin=true
#
# Look for the Apple JDKs first to preserve the existing behaviour, and then look
# for the new JDKs provided by Oracle.
#
if [[ -z "$JAVA_HOME" && -L /System/Library/Frameworks/JavaVM.framework/Versions/CurrentJDK ]] ; then
#
# Apple JDKs
#
export JAVA_HOME=/System/Library/Frameworks/JavaVM.framework/Versions/CurrentJDK/Home
fi

if [[ -z "$JAVA_HOME" && -L /System/Library/Java/JavaVirtualMachines/CurrentJDK ]] ; then
#
# Apple JDKs
#
export JAVA_HOME=/System/Library/Java/JavaVirtualMachines/CurrentJDK/Contents/Home
fi

if [[ -z "$JAVA_HOME" && -L "/Library/Java/JavaVirtualMachines/CurrentJDK" ]] ; then
#
# Oracle JDKs
#
export JAVA_HOME=/Library/Java/JavaVirtualMachines/CurrentJDK/Contents/Home
fi
;;
esac
if [ -z "$JAVA_HOME" ] ; then
if [ -r /etc/gentoo-release ] ; then
JAVA_HOME=`java-config --jre-home`
fi
fi
#此处貌似是为了照顾gentoo这个操作系统，特别加的，属于适应各操作系统方面的代码
if [ -z "$M2_HOME" ] ; then
## resolve links - $0 may be a link to maven's home
PRG="$0"
#$0 ----当前shell名
# need this for relative symlinks
#test –h File    文件存在并且是一个符号链接（同-L）
while [ -h "$PRG" ] ; do
ls=`ls -ld "$PRG"`
link=`expr "$ls" : '.*-> \(.*\)$'`
if expr "$link" : '/.*' > /dev/null; then
PRG="$link"
else
PRG="`dirname "$PRG"`/$link"
fi
done
#这个是排除软链接，找出真实的命令运行目录
#如果有童鞋分析过tomcat的startup.sh脚本，就可以发现，上面的脚本基本雷同

saveddir=`pwd`
M2_HOME=`dirname "$PRG"`/..
# make it fully qualified
M2_HOME=`cd "$M2_HOME" && pwd`
cd "$saveddir"
# echo Using m2 at $M2_HOME
fi
#cd进入mvn的应用目录
# For Cygwin, ensure paths are in UNIX format before anything is touched
if $cygwin ; then
[ -n "$M2_HOME" ] &&
M2_HOME=`cygpath --unix "$M2_HOME"`
[ -n "$JAVA_HOME" ] &&
JAVA_HOME=`cygpath --unix "$JAVA_HOME"`
[ -n "$CLASSPATH" ] &&
CLASSPATH=`cygpath --path --unix "$CLASSPATH"`
fi
# For Migwn, ensure paths are in UNIX format before anything is touched
if $mingw ; then
[ -n "$M2_HOME" ] &&
M2_HOME="`(cd "$M2_HOME"; pwd)`"
[ -n "$JAVA_HOME" ] &&
JAVA_HOME="`(cd "$JAVA_HOME"; pwd)`"
# TODO classpath?
fi
#上面一大串都是适应mingw和cygwin环境的，直接略过，下面才是干货
#test –z 字符串 字符串的长度为零
#如果没有设置JAVA_HOME，程序就自己去找JAVA_HOME
if [ -z "$JAVA_HOME" ]; then
javaExecutable="`which javac`"
if [ -n "$javaExecutable" -a ! "`expr \"$javaExecutable\" : '\([^ ]*\)'`" = "no" ]; then
#test –n 字符串的长度非零
#test 表达式1 –a 表达式2  两个表达式都为真
#link=`expr "$ls" : '.*-> \(.*\)$'` 模拟后： expr 'lrwxrwxrwx 1 root root 19 3月  17 10:12 ./bbb.sh -> /root/shell/test.sh' : '.*-> \(.*\)$'
#很明确的发现是用expr来提取/root/shell/test.sh的内容
#而这个循环就可以明确其目的，排除命令为链接，找出命令真正的目录，防止后面的命令出错
# readlink(1) is not available as standard on Solaris 10.
#[^]            # 匹配不在指定组内的字符
#上面的判读，主要是判断which javac，是否存在....
readLink=`which readlink`
if [ ! `expr "$readLink" : '\([^ ]*\)'` = "no" ]; then
javaExecutable="`readlink -f \"$javaExecutable\"`"
javaHome="`dirname \"$javaExecutable\"`"
javaHome=`expr "$javaHome" : '\(.*\)/bin'`
JAVA_HOME="$javaHome"
export JAVA_HOME
fi
fi
fi
#如果没有设置JAVACMD，脚本就会在JAVA_HOME目录下去找
if [ -z "$JAVACMD" ] ; then
if [ -n "$JAVA_HOME"  ] ; then
if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
# IBM's JDK on AIX uses strange locations for the executables
JAVACMD="$JAVA_HOME/jre/sh/java"
else
JAVACMD="$JAVA_HOME/bin/java"
fi
else
JAVACMD="`which java`"
fi
fi
#test –x File  文件存在并且可执行
#javac命令用不了，那就报错了鸟~~~
if [ ! -x "$JAVACMD" ] ; then
echo "Error: JAVA_HOME is not defined correctly."
echo "  We cannot execute $JAVACMD"
exit 1
fi
#没有定义JAVA_HOME，脚本有自己找不到，就会在这里报错
if [ -z "$JAVA_HOME" ] ; then
echo "Warning: JAVA_HOME environment variable is not set."
fi
CLASSWORLDS_LAUNCHER=org.codehaus.plexus.classworlds.launcher.Launcher
# For Cygwin, switch paths to Windows format before running java
if $cygwin; then
[ -n "$M2_HOME" ] &&
M2_HOME=`cygpath --path --windows "$M2_HOME"`
[ -n "$JAVA_HOME" ] &&
JAVA_HOME=`cygpath --path --windows "$JAVA_HOME"`
[ -n "$CLASSPATH" ] &&
CLASSPATH=`cygpath --path --windows "$CLASSPATH"`
fi
#上面一堆代码的目的，就是为了下面一句代码提供变量.....
exec "$JAVACMD" \
$MAVEN_OPTS \
-classpath "${M2_HOME}"/boot/plexus-classworlds-*.jar \
"-Dclassworlds.conf=${M2_HOME}/bin/m2.conf" \
"-Dmaven.home=${M2_HOME}"  \
${CLASSWORLDS_LAUNCHER} "$@"