1 条件判断  if
if test -f "$1"
then
echo "$1 is a file"
elif test -d "$1"
then
(cd "$1";pwd;echo "$1 is a directory")
else
echo "$1 is neither a file or a directory"
fi
注意 每个if 后面都有一个then ，
第二个条件用 elif ，
结尾用fi
2 条件判断case
case $1 in
(*.c)
echo "c file" ;;
(*.txt)
echo "txt file" ;;
(*)
echo "unknown file";;
esac
注意结尾要用esac ， case后执行要用两个；；

3 while循环

i=0;
sum=0;
 
while true
do
i=`expr $i + 1`
sum=`expr $sum + $i`
if [ $i = "100" ]
then break
fi
done
echo $i $sum
注意 while后要有do ， done ， 执行表达式用用`` ， 数学运算要用expr ， if后面跟表达式要用[]， 而且里面的句子一定要跟[和] 有空格。
还有while跟until的区别
until [ $i = "100" ]   和  while [ $i ！= "100" ]
注意不能用< >, 这里是输入输出的意思。
大于小于用 -gt -lt 表示

4 for循环

  已经跟经理提出离职了，趁还在公司的这段时间整理一些在linux下工作积累的经验。

<?xml version = "1.0" encoding="GB2312" ?>
<project default = "main" basedir = "." >
 <property name = "srcpath" value = "sdkongkong"/>
 <property name = "classpath" value = "build/classes"/>
 <target name = "init">
   <mkdir dir = "${classpath}"/>
 </target>
 <target name = "main" depends = "init">
   <javac srcdir = "${srcpath}" destdir = "${classpath}"/>
 </target>
 <target name = "clean" descrīption = "clean old class">
   <delete dir ="${classpath}"/>
 </target>
</project>

WebPageReader.java

package sdkongkong;
   import java.net.URL;
   import java.net.MalformedURLException;
   import java.net.URLConnection;
   import java.io.IOException;
   import java.io.BufferedReader;
   import java.io.InputStreamReader;

   public class WebPageReader {

      private static URLConnection connection;

      private static void connect( String urlString ) {
        try {
          URL url = new URL(urlString);
          connection = url.openConnection();
          System.out.println(connection.getClass());
        } catch (MalformedURLException e){
          e.printStackTrace();
        } catch (IOException e) {
          e.printStackTrace();
        }
      }

      private static void readContents() {
        BufferedReader in = null;
        try {
          in = new BufferedReader(
            new InputStreamReader(
              connection.getInputStream()));

          String inputLine;
          while (
            (inputLine = in.readLine()) != null) {
            System.out.println(inputLine);
          }
        } catch (IOException e) {
          e.printStackTrace();
        }
      }

      public static void main(String[] args) {
        if (args.length != 1) {
          System.err.println("usage: java WebPageReader " + "<url>");
          System.exit(0);
        }
        connect(args[0]);
        readContents();
      }
   }

 

使用方法,java WebPageReader + url(http://www.sina.com)