【>】  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