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

 for var in list
 do
     commands
 done

 oracle@suse:~/testshell> cat fortest.sh
 #!/bin/bash
 #test for command

 for city in beijing shanghai shenzhen dalian
 do
     echo the  city is $city
 done
 oracle@suse:~/testshell> ./fortest.sh
 the city is beijing
 the city is shanghai
 the city is shenzhen
 the city is dalian

一种c语言风格的for命令

 for (( variable assignment ; condition ; iterationprocess ))
 do
      commands
 done

 oracle@suse:~/testshell> cat fortest.sh
 #!/bin/bash
 #test for command

 sum=
 for (( i=;i<=;i++ ))
 do
     (( sum = sum + i ))

 done
 echo sum= $sum

 for (( a=,b=;a<,b<;a++,b++ ))
 do
     (( c = a + b ))
     echo c = $c
 done
 oracle@suse:~/testshell> ./fortest.sh
 sum=
 c =
 c = 

2.while命令基本格式

 while test command
 do
     other commands
 done

 oracle@suse:~/testshell> cat whiletest.sh
 #!/bin/bash
 #test while command

 var=

 while [ $var -gt  ]
 do
     (( var = var - ))
     echo var = $var
 done
 oracle@suse:~/testshell> ./whiletest.sh
 var =
 var =
 var = 

3.until命令基本格式

 until test commands
 do
     other commands
 done

 oracle@suse:~/testshell> cat untiltest.sh
 #!/bin/bash
 #test until command

 var=

 until [ $var -gt  ]
 do
     (( var++ ))
     echo var = $var
 done
 oracle@suse:~/testshell> ./untiltest.sh
 var =
 var =
 var =
 var = 

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

 oracle@suse:~/testshell> cat untiltest.sh
 #!/bin/bash
 #test until command

 var=

 until [ $var -gt  ]
 do
     (( var++ ))
     echo var = $var
 done > result.txt
 oracle@suse:~/testshell> ./untiltest.sh
 oracle@suse:~/testshell> ls
 untiltest.sh     result.txt
 oracle@suse:~/testshell> cat result.txt
 var =
 var =
 var =
 var =