linux shell脚本使用结构化命令(2)

一.for命令

二.while命令

三.until命令

1.for命令基本格式

1 for var in list
2 do
3     commands
4 done

 1 [email protected]:~/testshell> cat fortest.sh
 2 #!/bin/bash
 3 #test for command
 4
 5 for city in beijing shanghai shenzhen dalian
 6 do
 7     echo the  city is $city
 8 done
 9 [email protected]:~/testshell> ./fortest.sh
10 the city is beijing
11 the city is shanghai
12 the city is shenzhen
13 the city is dalian

一种c语言风格的for命令

1 for (( variable assignment ; condition ; iterationprocess ))
2 do
3      commands
4 done

 1 [email protected]:~/testshell> cat fortest.sh
 2 #!/bin/bash
 3 #test for command
 4
 5 sum=0
 6 for (( i=1;i<=100;i++ ))
 7 do
 8     (( sum = sum + i ))
 9
10 done
11 echo sum= $sum
12
13 for (( a=1,b=1;a<5,b<3;a++,b++ ))
14 do
15     (( c = a + b ))
16     echo c = $c
17 done
18 [email protected]:~/testshell> ./fortest.sh
19 sum= 5050
20 c = 2
21 c = 4

2.while命令基本格式

1 while test command
2 do
3     other commands
4 done

 1 [email protected]:~/testshell> cat whiletest.sh
 2 #!/bin/bash
 3 #test while command
 4
 5 var=3
 6
 7 while [ $var -gt 0 ]
 8 do
 9     (( var = var -1 ))
10     echo var = $var
11 done
12 [email protected]:~/testshell> ./whiletest.sh
13 var = 2
14 var = 1
15 var = 0

3.until命令基本格式

1 until test commands
2 do
3     other commands
4 done

 1 [email protected]:~/testshell> cat untiltest.sh
 2 #!/bin/bash
 3 #test until command
 4
 5 var=5
 6
 7 until [ $var -gt 8 ]
 8 do
 9     (( var++ ))
10     echo var = $var
11 done
12 [email protected]:~/testshell> ./untiltest.sh
13 var = 6
14 var = 7
15 var = 8
16 var = 9

还有一点就是循环输出可以输出到屏幕，也可以输出到文件，就是在done命令后加个处理命令

 1 [email protected]:~/testshell> cat untiltest.sh
 2 #!/bin/bash
 3 #test until command
 4
 5 var=5
 6
 7 until [ $var -gt 8 ]
 8 do
 9     (( var++ ))
10     echo var = $var
11 done > result.txt
12 [email protected]:~/testshell> ./untiltest.sh
13 [email protected]:~/testshell> ls
14 untiltest.sh     result.txt
15 [email protected]:~/testshell> cat result.txt
16 var = 6
17 var = 7
18 var = 8
19 var = 9