9.3.3 输出重定向

--标准输入输出

键盘——/dev/stdin 文件描述符为0

显示器——/dev/sdtout 文件描述符为1

显示器——/dev/sdterr 文件描述符为2，类型是标准错误输出

背就背文件描述符就好了

--输出重定向

就是把原本应该标准输出的方向重新定向到文件（拐个弯）。

用处就是自动的记录等，有实际的用处，也常用。

比如

[root@andy ~]# ifconfig > test.log
[root@andy ~]# cat test.log
eth0 Link encap:Ethernet HWaddr 00:0C:29:61:EB:6B
inet addr:192.168.23.50 Bcast:192.168.23.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fe61:eb6b/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:11069 errors:0 dropped:0 overruns:0 frame:0
TX packets:3521 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:798686 (779.9 KiB) TX bytes:447837 (437.3 KiB)
Interrupt:19 Base address:0x2000

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:20 errors:0 dropped:0 overruns:0 frame:0
TX packets:20 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:1532 (1.4 KiB) TX bytes:1532 (1.4 KiB)

命令的执行，可能会是定时用户来做的。

[root@andy ~]# ls > test.log
[root@andy ~]# cat test.log
anaconda-ks.cfg
cangls
hello.sh
install.log
install.log.syslog
japan
test.log

单个>，会覆盖结果；双>>是追加

[root@andy ~]# ifconfig >> test.log
[root@andy ~]# cat test.log
anaconda-ks.cfg
cangls
hello.sh
install.log
install.log.syslog
japan
test.log
eth0 Link encap:Ethernet HWaddr 00:0C:29:61:EB:6B
inet addr:192.168.23.50 Bcast:192.168.23.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fe61:eb6b/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:11238 errors:0 dropped:0 overruns:0 frame:0
TX packets:3586 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:811445 (792.4 KiB) TX bytes:455539 (444.8 KiB)
Interrupt:19 Base address:0x2000

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:20 errors:0 dropped:0 overruns:0 frame:0
TX packets:20 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:1532 (1.4 KiB) TX bytes:1532 (1.4 KiB)

如果希望同时保存报错信息（犯2信息）

dateads 2>>test.log

另外注意，追加是有空格，错误输出是没有空格的2>>test.log

但是，最有用的是正确和错误都要

命令 >> 文件 2>&1  

命令 &>> 文件  ——写到同一个文件

[root@andy ~]#
[root@andy ~]# ifconfig >> test2.log 2>&1
[root@andy ~]# cat test2.log
eth0 Link encap:Ethernet HWaddr 00:0C:29:61:EB:6B
inet addr:192.168.23.50 Bcast:192.168.23.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fe61:eb6b/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:11444 errors:0 dropped:0 overruns:0 frame:0
TX packets:3638 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:825629 (806.2 KiB) TX bytes:461351 (450.5 KiB)
Interrupt:19 Base address:0x2000

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:20 errors:0 dropped:0 overruns:0 frame:0
TX packets:20 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:1532 (1.4 KiB) TX bytes:1532 (1.4 KiB)