【>】 替换
【>>】追加
【1】 正确
【2】 错误 不要错误输出可采用2>/dev/dev/null
e.g
mj@monitor ~]$ ls
123 456
[mj@monitor ~]$ ls 789 >>123 2>>456
[mj@monitor ~]$ cat 123
[mj@monitor ~]$ cat 456
ls: 789: No such file or directory
[mj@monitor ~]$ ls 123 >>123 2>>456
[mj@monitor ~]$ cat 123
123
[mj@monitor ~]$ cat 456
ls: 789: No such file or directory
[mj@monitor ~]$ ls 0 >>123 2>>456
[mj@monitor ~]$ cat 456
ls: 789: No such file or directory
ls: 0: No such file or directory
[mj@monitor ~]$ cat 123
123
例子很清楚,道理很简单。2就是错误输出,1是正确输出默认隐藏。
【<】 由文件输出
e.g
[mj@monitor ~]$ ls
[mj@monitor ~]$ echo "test">a
[mj@monitor ~]$ cat > b < a
[mj@monitor ~]$ cat b
test
明白啦!
【<<】截止到输出某个指定的内容便执行退出
[mj@monitor ~]$ cat > a << stop #此处stop是指定内容
> sdasd
> sdfsrgsrgf
> dgstgsdfsd
> exit
> quit
> fadkad
> stop
[mj@monitor ~]$ echo a <<exit #此处exit是指定内容
> sdasd
> sdasfasd
> dfadsa
> fasdada
> fasdas
> exit
a