shell编程中for，while，util，case，select，break， continue用法详解

#!/bin/bash
# Program:
#       This program will show the use of if
# History:
# 2015/1/8 Alex First release
i=10
while [[ $i -gt 5 ]]
do
        echo $i
        i=`expr $i - 1`;            
done
exit 0
注意：在Shell中四则运算不能简简单单的加减乘除，应该要写如下的格式： val1=`$val2 - 1`
其中“=”后面用“`”包住表达式，这个符号在Shell中十分有用，是Tab键上面“~”的原来形式。可以用来将很多命令的结果保存到一个变量中去。接着就是运算符了，运算符的左右两边必须是空格，否则会出错。

deyuy/bin/my_shell >> ./while1.sh
10
9
8
7
6

注意：　　１.expr命令的用法请参考　http://blog.chinaunix.net/uid-25880122-id-2937521.html
　　　　　２.``的作用是运行``之间的命令,并且将命令运行的结果返回。详细请参考：http://blog.csdn.net/miyatang/article/details/8077123
　　　　　３.　更多while实例参考：http://blog.csdn.net/firefoxbug/article/details/7237319

#!/bin/bash
# Program:
#       This program will show the use of for
# History:
# 2015/1/12 First release
# 自定义列表
for loop in 1 2 3 4 5
do
        echo "loop=$loop"
done
exit 0

deyuy/bin/my_shell >> chmod u+x for1.sh
deyuy/bin/my_shell >> ./for1.sh
loop=1
loop=2
loop=3
loop=4
loop=5

还可以通过读取文件内容生成变量列表

deyuy/bin/my_shell >> vim num.txt
1 2 3 4 5
6
7
8
#!/bin/bash
# Program:
# This program will show the use of for
# History:
# 2015/1/12 First release
# 以命令返回值作为列表
i=0
for i in `cat num.txt`
do
echo "i=$i"
done
exit 0
deyuy/bin/my_shell >> ./for1.sh
i=1
i=2
i=3
i=4
i=5
i=6
i=7
i=8

#!/bin/bash
# Program:
#       This program will show the use of for
# History:
# 2015/1/12 First release
# 自定义列表：带引号
i=0
for loop in "apple hhhh bbbb eeee"
do
　　　　 i=`expr $i + 1`
        echo "loop=$loop"
　　　　 echo "count=$i"
done
exit 0

deyuy/bin/my_shell >> chmod u+x for4.sh
deyuy/bin/my_shell >> ./for4.sh
loop=apple hhhh bbbb eeee
count=1
说明：从结果可以看出for循环打印字符串到结束,包括空格,只执行了一次。如果把 in列表改为 for loop in "apple" "hhhh" "bbbb" "eeee"
则输出结果为

loop=apple
count=1
loop=hhhh
count=2
loop=bbbb
count=3
loop=eeee
count=4

#!/bin/bash
# Program:
#       This program will show the use of for
# History:
# 2015/1/12 First release
# 自定义列表，不带引号
i=0
for loop in apple hhhh bbbb eeeedo
　　　　i=`expr $i + 1`
            echo "loop=$loop"
　　　   echo "count=$i"　 
done

exit 0

deyuy/bin/my_shell >> ./for4.sh
loop=apple
count=1
loop=hhhh
count=2
loop=bbbb
count=3
loop=eeee
count=4
注意：对比两张方式输出的不同可以看出，如果用户想让把空格分割的每个单词都输出要通过第二种方式。        

# Program:
#       This program will show the use of for
# History:
# 2015/1/12 First release
for loop in `ls`
do
        echo "$loop"
done
exit 0

deyuy/bin/my_shell >> sh for2.sh
app1
for1.sh
for2.sh
fun1.sh
hello.sh
hh.sh
if.sh
if2.sh
test.sh
test2.sh
var.sh
while1.sh

#!/bin/bash
# Program:
#       This program will show the use of for 
#       统计当前目录下文件数
# History:
# 2015/1/12 First release
counter=0
for files in *
do
        counter=`expr $counter + 1`
done
echo "There are $counter files in `pwd` directory."
exit 0

deyuy/bin/my_shell >> sh for3.sh
There are 13 files in /home/deyuy/bin/my_shell directory.

#!/bin/bash
# Program:
#       This program will show the use of for
# History:
# 2015/1/13 release
i=0
for params
do
        i=`expr $i + 1`
        echo "You supplied $params as a command line option"
        echo "count=$i"
done
        echo $params

exit 0

deyuy/bin/my_shell >> ./for5.sh p1 p2 p3
You supplied p1 as a command line option
count=1
You supplied p2 as a command line option
count=2
You supplied p3 as a command line option
count=3
p3
下面的脚本包含i n"$ @"，结果与上面的脚本相同。
#!/bin/bash
# Program:
#       This program will show the use of for
# History:
# 2015/1/13 release
i=0
for params in "$@"
do
        i=`expr $i + 1`
        echo "You supplied $params as a command line option"
        echo "count=$i"
done
        echo $params

exit 0

deyuy/bin/my_shell >> ./for5.sh p1 p2 p3
You supplied p1 as a command line option
count=1
You supplied p2 as a command line option
count=2
You supplied p3 as a command line option
count=3
p3
下面的脚本包含i n"$ *"，结果与上面的脚本不同。
#!/bin/bash
# Program:
#       This program will show the use of for
# History:
# 2015/1/13 release
i=0
for params in "$*"
do
        i=`expr $i + 1`
        echo "You supplied $params as a command line option"
        echo "count=$i"
done
        echo $params

exit 0


deyuy/bin/my_shell >> ./for5.sh p1 p2 p3
You supplied p1 p2 p3 as a command line option
count=1
p1 p2 p3
说明：关于$@和$*的区别请参考http://www.cnblogs.com/yuexiaxiaoxi/articles/4203609.html

#!/bin/bash
# Program:
#       This program will show the use of for
# History:
# 2015/1/13 release
APPS="/apps/accts /apps/claims /apps/stock /apps/serv"
SCRIPTS="audit.check report.run cleanup"
MY_DATE=`date +%H:%M" on "%d/%m/%Y`
i=0
j=0
#outer loop
for loop in $APPS
do
        i=`expr $i + 1`
#inner loop
        for loop2 in $SCRIPTS
        do
                j=`expr $i + 1`
                echo "system $loop now running $loop2 at $MY_DATE"
                echo "inner loop counter=$j"
        done
        echo "outer loop counter=$i"
done
        echo $params


deyuy/bin/my_shell >> ./for6.sh
system /apps/accts now running audit.check at 20:53 on 12/01/2015
inner loop counter=2
system /apps/accts now running report.run at 20:53 on 12/01/2015
inner loop counter=2
system /apps/accts now running cleanup at 20:53 on 12/01/2015
inner loop counter=2
outer loop counter=1
system /apps/claims now running audit.check at 20:53 on 12/01/2015
inner loop counter=3
system /apps/claims now running report.run at 20:53 on 12/01/2015
inner loop counter=3
system /apps/claims now running cleanup at 20:53 on 12/01/2015
inner loop counter=3
outer loop counter=2
system /apps/stock now running audit.check at 20:53 on 12/01/2015
inner loop counter=4
system /apps/stock now running report.run at 20:53 on 12/01/2015
inner loop counter=4
system /apps/stock now running cleanup at 20:53 on 12/01/2015
inner loop counter=4
outer loop counter=3
system /apps/serv now running audit.check at 20:53 on 12/01/2015
inner loop counter=5
system /apps/serv now running report.run at 20:53 on 12/01/2015
inner loop counter=5
system /apps/serv now running cleanup at 20:53 on 12/01/2015
inner loop counter=5
outer loop counter=4