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2013/11/18 01:12
文件描述符 缩写 描述
0 STDIN 标准输入
1 STDOUT 标准输出
2 STDERR 标准错误
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重定向错误输出
#ls -al badfile 2> test4
#cat test4
ls: cannot access badfile: No such file or directory
用这种方法shell只会重定向错误信息，而非普通数据。
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重定向错误和正常输出，必须用两个重定向符号。
ls -al test test2 test3 badtest 2> test6 1> test7
test 真是存在
cat test6
[root@localhost ~]# cat test7
-rw-r--r-- 1 root root 22 11-21 09:29 test
root@localhost ~]# cat test6
s: test2: 娌℃湁閭ｄ釜鏂囦欢鎴栫洰褰?
s: test3: 娌℃湁閭ｄ釜鏂囦欢鎴栫洰褰?
s: badtest: 娌℃湁閭ｄ釜鏂囦欢鎴栫洰褰?
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如果想要STDERR和 STDOUT输出重定向到同一个输出文件。
则可以使用 &>
并且显示出来的错误信息优先级大于普通信息会被优先显示。
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日志中心clean清理根目录
[root@localhost ~]# cat tet
#!/bin/bash
echo "This is an error message" >&2
echo "This is an normal output"
[root@localhost ~]# sh tet
This is an error message
This is an normal output
[root@localhost ~]# sh tet 2> ts
This is an normal output
[root@localhost ~]# cat ts
This is an error message
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[root@aoi ~]# cat t
#!/bin/bash
exec 0< testfile
count=1
while read line
do
echo "Line #$count: $line"
count=$[ $count + 1]
done
[root@aoi ~]# sh t
Line #1: dds
Line #2: faf
Line #3: asfas
Line #4: fsa
Line #5:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
创建输出文件描述符 自定义
[root@aoi ~]# cat r
#!/bin/bash
exec 3>test3out
echo "this should display on the monitor"
echo " and this should be stored in the file" >&3
echo "Then this should be back on the monitor"
[root@aoi ~]# sh r
this should display on the monitor
Then this should be back on the monitor
[root@aoi ~]# cat test3out
and this should be stored in the file
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[root@aoi ~]# cat f
#!/bin/bash
exec 3>&1
exec 1>test4out
echo "This should store in the output file"
echo " a long with this line."
exec 1>&3
echo "Now thins should be back to normal"
[root@aoi ~]# sh f
Now thins should be back to normal
[root@aoi ~]# cat test4out
This should store in the output file
a long with this line.
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[root@localhost ~]# cat 5
#!/bin/bash
exec 6<&0
exec 0< t
count=1
while read line
do
echo "Line #$count: $line"
count=$[ $count + 1 ]
done
exec 0<&6
read -p "Are you done now?" answer
case $answer in
Y|y) echo "GOODbey";;
N|n) echo "SOrry,this the end";;
esac
[root@localhost ~]# sh 5
Line #1: dsafdds
Line #2: sfas
Line #3: safdasbv
Are you done now?n
SOrry,this the end
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[root@localhost ~]# cat 6
#!/bin/bash
exec 3<> t
read line <&3
echo "Read: $line"
echo "This is a test line" >&3
[root@localhost ~]# cat t
da1
da2
da3
da4
dafasfdsfsd
dasffdasfdasfdas
fasedafsdfasdfsd
[root@localhost ~]# sh 6
Read: da1
[root@localhost ~]# cat t
da1
This is a test line
fsd
dasffdasfdasfdas
fasedafsdfasdfsd
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[root@localhost ~]# cat 7
#!/bin/bash
exec 3> t
echo "This is a test line of data" >&3
exec 3>&-
cat t
exec 3> t
echo "This'll be bad" >&3
[root@localhost ~]# cat t
da1
This is a test line
fsd
dasffdasfdasfdas
fasedafsdfasdfsd
[root@localhost ~]# sh 7
This is a test line of data
[root@localhost ~]# cat t
This'll be bad
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[root@localhost ~]# cat 8
#!/bin/bash
exec 3> testfile1
exec 6> testfile2
exec 7< test
lsof -a -p $$ -d0,1,2,3,6,7
[root@localhost ~]# sh 8
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
sh 874 root 0u CHR 136,0 0t0 2 /dev/pts/0
sh 874 root 1u CHR 136,0 0t0 2 /dev/pts/0
sh 874 root 2u CHR 136,0 0t0 2 /dev/pts/0
sh 874 root 3w REG 253,0 0 65648 /root/testfile1
sh 874 root 6w REG 253,0 0 65654 /root/testfile2
sh 874 root 7r REG 253,0 22 65642 /root/tests
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[root@localhost ~]# cat t
fasdfd
fdasasf
fdsafasasdf
fdasasdfasd
fa
sdfdassf
[root@localhost ~]# cat /dev/null >t
[root@localhost ~]# cat t
将/dev/null作为输入文件，可以快速移除现有文件中的数据而不用先删除文件再创建。
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