请教各位高手，下面这两行语句是什么意思？

wang_yilun

这个脚本中我现在对这两行不明白，请各位高手指点一下。
link=`expr "$ls" : '.*-> \(.*\)$'`
  if expr "$link" : '.*/.*' > /dev/null; then

这是tomcat中的startup.sh脚本
完整的如下：
#!/bin/sh
# -----------------------------------------------------------------------------
# Start Script for the CATALINA Server
#
# $Id: startup.sh,v 1.3 2002/08/04 18:19:43 patrickl Exp $
# -----------------------------------------------------------------------------

# resolve links - $0 may be a softlink
PRG="$0"

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

PRGDIR=`dirname "$PRG"`
EXECUTABLE=catalina.sh

# Check that target executable exists
if [ ! -x "$PRGDIR"/"$EXECUTABLE" ]; then
  echo "Cannot find $PRGDIR/$EXECUTABLE"
  echo "This file is needed to run this program"
  exit 1
fi

exec "$PRGDIR"/"$EXECUTABLE" start "$@"

还有就是while [ -h "$PRG" ] 中的 -h 是什么含义？

waker

link=`expr "$ls" : '.*-> \(.*\)$'`

在变量ls匹配表达式.*-> \(.*\)$
如果匹配，将\(.*\)中与.*匹配的字串取出赋值给变量link

waker

如果写成sed可能会好理解一点
link=$(echo "$ls"|sed -n 's/.*->\(.*\)$/\1/p')