164 lines
2.1 KiB
Markdown
164 lines
2.1 KiB
Markdown
### 概览
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- 列表循环：用于将一组命令执行已知的次数
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- 不带列表循环，执行时由用户指定参数和参数的个数
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- 类C风格循环
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- break continue exit
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-
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### 列表循环
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- 方式一
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```shell
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# 无步长
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for variable in {list}
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do
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command1
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command2
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...
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done
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# 有步长
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for variable in {list..步长}
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do
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command1
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command2
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...
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done
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```
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- 方式二
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```
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for variable in a b c
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do
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command1
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command2
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...
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done
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```
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- 示例
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```
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#! /bin/env bash
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# 步长为2
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for i in {1..5..2}
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do
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echo $i
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done
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#! /bin/env bash
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for i in 1 2 3 4 5
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do
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echo $i
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done
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```
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### 不带列表循环
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- 方式一
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```
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for variable
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do
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command
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command
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...
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done
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```
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- 示例
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```
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#! /bin/env bash
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for i
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do
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echo hello
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done
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```
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- 自动用$@ 用户输入的所有参数进行循环
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```
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me@me-EQ59:~/shell_demo/scripts/shell01$ bash -x for_not_list.sh a b c
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+ for i in "$@"
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+ echo hello
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hello
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+ for i in "$@"
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+ echo hello
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hello
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+ for i in "$@"
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+ echo hello
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hello
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me@me-EQ59:~/shell_demo/scripts/shell01$
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```
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```
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me@me-EQ59:~/shell_demo/scripts/shell01$ bash -x for_not_list.sh {1..5}
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+ for i in "$@"
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+ echo hello
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hello
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+ for i in "$@"
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+ echo hello
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hello
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+ for i in "$@"
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+ echo hello
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hello
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+ for i in "$@"
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+ echo hello
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hello
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+ for i in "$@"
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+ echo hello
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hello
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me@me-EQ59:~/shell_demo/scripts/shell01$
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```
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```
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me@me-EQ59:~/shell_demo/scripts/shell01$ bash -x for_not_list.sh `seq 5`
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+ for i in "$@"
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+ echo hello
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hello
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+ for i in "$@"
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+ echo hello
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hello
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+ for i in "$@"
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+ echo hello
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hello
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+ for i in "$@"
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+ echo hello
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hello
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+ for i in "$@"
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+ echo hello
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hello
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me@me-EQ59:~/shell_demo/scripts/shell01$
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```
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### 类C风格循环
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- 方式一
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```
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# expr1 定义变量并赋初值
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# expr 决定是否进行循环
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# expr3 决定循环变量如何改变，决定循环什么时候退出
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for (( expr1;expr2;expr4 ))
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do
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command
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command
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...
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done
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```
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- 示例
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```
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for (( i=1;i<=5;i++ ))
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do
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echo $i
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done
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```
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```
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me@me-EQ59:~/shell_demo/scripts/shell01$ for ((i=0;i<=5;i++));do echo $i;done
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0
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1
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2
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3
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4
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5
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me@me-EQ59:~/shell_demo/scripts/shell01$ for ((i=0;i<=5;i++));do [ $((i%2)) -eq 0 ] && echo $i;done
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0
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2
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4
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me@me-EQ59:~/shell_demo/scripts/shell01$
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``` |