重定向一览

重定向，我喜欢。

文件描述符：

标准输入：0；标准输出：1；标准错误：2；

重定向符：

>file：重定向标准输出到file

<file：从file接受标准输入

>>file：重定向标准输出到file，如果file存在则附加输出到file

>|file：即使设置了noclobber仍强制标准输出到file

<>file：file同时作为标准输入与标准输出

<<label：here-document，以shell为标准输入，即屏幕输入为标准输入，直至独到含有label的行

e.g.

xk@linux:~/work> cat >>a.sh<<eof

> this is the test text

> for <<

> eof

xk@linux:~/work> cat a.sh

this is the test text

for <<

xk@linux:~/work>

n>file：将文件描述符n重定向到file

e.g.

xk@linux:~/work> cat s.sh

#!/bin/bash

PS3="which is your hobby? Please select:"

OPTIONS="computer:music:math:art"

OIFS=$IFS

IFS=:

select selected in $OPTIONS;do

        case $selected in

                computer) echo "you select 1";;

                music) echo  "you select 2";;

                math) echo "you select math";;

                art) echo "you select art";;

                *) echo "error";exit 1;;

        esac

done

xk@linux:~/work> ./s.sh 1>out 2>error

3

6

xk@linux:~/work> cat out

you select math

error

xk@linux:~/work> cat error

1) computer

2) music

3) math

4) art

which is your hobby? Please select:which is your hobby? Please select:xk@linux:~/work>

这里也可以看出select的提示信息是通过标准错误输出的。

xk@linux:~/work> lkajdflk 2>out

xk@linux:~/work> cat out

-bash: lkajdflk: command not found

&>file：重定向标准输出和标准错误到file

e.g.

xk@linux:~/work> cat s.sh

#!/bin/bash

PS3="which is your hobby? Please select:"

OPTIONS="computer:music:math:art"

OIFS=$IFS

IFS=:

select selected in $OPTIONS;do

        case $selected in

                computer) echo "you select 1";;

                music) echo  "you select 2";;

                math) echo "you select math";;

                art) echo "you select art";;

                *) echo "error";exit 1;;

        esac

done

xk@linux:~/work> rm error.bak

xk@linux:~/work> ./s.sh &>error.bak

3

6

xk@linux:~/work> cat error.bak

1) computer

2) music

3) math

4) art

which is your hobby? Please select:you select math

which is your hobby? Please select:error

xk@linux:~/work>

n>&m：将文件描述符n发送到与文件描述符m相同的位置（文件或管道等）

e.g.

xk@linux:~/work> lkjaldskfjlk 2>error 1>out 2>&1

xk@linux:~/work> cat out

-bash: lkjaldskfjlk: command not found

xk@linux:~/work> cat error

xk@linux:~/work>

可见标准错误被以标准输出的形式传出。继续，

xk@linux:~/work> cat out 2>error 1>>out 1>&2

xk@linux:~/work> cat out

-bash: lkjaldskfjlk: command not found

xk@linux:~/work> cat error

-bash: lkjaldskfjlk: command not found

xk@linux:~/work>

这里标准输出又被以标准错误的形式传出。