经常会遇到这种情况，要对一批文件挨个进行处理，又不想写一个脚本，
例如查找所有的jar包中是否存在特定的类
for f in `ls *.jar`; do jar tvf $f|grep FileAlreadyExistsException; done
注意如果使用for f in ‘*.jar’ 那么$f则是所有文件的拼接，不会产生正确的结果
再优化一下，输出jar文件名，注意用;分割语句
for f in `ls *.jar`; do echo $f; jar tvf $f|grep FileAlreadyExistsException; done
bash中的for循环有几种方式：
1.for name [ in word ] ; do list ; done
2.for (( expr1 ; expr2 ; expr3 )) ; do list ; done//注意有2层括号
其中list简单说就是一串由操作符（operator ；、&、&&、||）分隔开的管道（pipeline）序列，详情参看man bash
各给出一个简单例子：
1.
for filename in `ls`
do
cat $filename
done
2.
for((i=0; i<10; i++))
do
echo $i
done
3.每次减1
for (( i = 300; i >= 1 ;i– ))
do
#echo -ne “`date ‘+%T’` ”
echo -ne “$i ”
sleep 1
done
5. 每次减5
for (( i = 300; i >= 1 ;i– ))
do
echo -ne “$i ”
i=$(expr \( $i – 4 \));
#sleep 5
done
1 #!/bin/bash
2 # Two ways to count up to 10.
3
4 echo
5
6 # Standard syntax.
7 for a in 1 2 3 4 5 6 7 8 9 10
8 do
9 echo -n “$a ”
10 done
11
12 echo; echo
13
14 # +==========================================+
15
16 # Now, let’s do the same, using C-like syntax.
17
18 LIMIT=10
19
20 for ((a=1; a <= LIMIT ; a++)) # Double parentheses, and “LIMIT” with no “$”.
21 do
22 echo -n “$a ”
23 done # A construct borrowed from ‘ksh93′.
24
25 echo; echo
26
27 # +=========================================================================+
28
29 # Let’s use the C “comma operator” to increment two variables simultaneously.
30
31 for ((a=1, b=1; a <= LIMIT ; a++, b++)) # The comma chains together operations.
32 do
33 echo -n “$a-$b ”
34 done
35
36 echo; echo
37
38 exit 0
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