grep实现的只是查找功能，而不能把查找的内容替换。以前vim操作文档的时候，可以查找也可以替换，但只限于在文本内部操作，而不能输出到屏幕上。sed工具以及后面要介绍的awk工具就能把替换的文本输出到屏幕上。

sed打印某行

sed命令的格式为：sed -n 'n'p filename，单引号内的n是一个数字，表示第几行。-n选项的作用是只显示要打印的行

[root@lizhipeng01 ~]# mkdir sed

[root@lizhipeng01 ~]# cd sed

[root@lizhipeng01 sed]# cp ../grep/passwd test.txt

[root@lizhipeng01 sed]# sed -n '/root/'p test.txt

root:x:0:0:root:/root:/bin/bash

operator:x:11:0:operator:/root:/sbin/nologin

[root@lizhipeng01 sed]# sed -nr '/r+t/'p test.txt         加上n不用脱意

[root@lizhipeng01 sed]# sed -nr '/o+t/'p test.txt

root:x:0:0:root:/root:/bin/bash

operator:x:11:0:operator:/root:/sbin/nologin

[root@lizhipeng01 sed]# sed -nr '/o{2}/'p test.txt    匹配2次o

root:x:0:0:root:/root:/bin/bash

lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin

mail:x:8:12:mail:/var/spool/mail:/sbin/nologin

operator:x:11:0:operator:/root:/sbin/nologin

postfix:x:89:89::/var/spool/postfix:/sbin/nologin

[root@lizhipeng01 sed]# sed -nr '/root|bus/'p test.txt      匹配root或者bus

root:x:0:0:root:/root:/bin/bash

operator:x:11:0:operator:/root:/sbin/nologin

dbus:x:81:81:System message bus:/:/sbin/nologin

[root@lizhipeng01 sed]# sed -n '2'p test.txt          打印第2行

bin:x:1:1:bin:/bin:/sbin/nologin

[root@lizhipeng01 sed]# sed -n '2,5'p test.txt       2到5行

bin:x:1:1:bin:/bin:/sbin/nologin

daemon:x:2:2:daemon:/sbin:/sbin/nologin

adm:x:3:4:adm:/var/adm:/sbin/nologin

lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin

[root@lizhipeng01 sed]# sed -n '1,$'p test.txt     从头到尾

sed命令加上-e选项可以实现多个行为

[root@lizhipeng01 sed]# sed -e '1'p -e '/bus/'p -n test.txt    先打印第一行，再打印匹配bus的行

root:x:0:0:root:/root:/bin/bash

dbus:x:81:81:System message bus:/:/sbin/nologin

[root@lizhipeng01 sed]# sed -e '1'p -e '/root/'p -n test.txt

root:x:0:0:root:/root:/bin/bash

root:x:0:0:root:/root:/bin/bash

operator:x:11:0:operator:/root:/sbin/nologin

[root@lizhipeng01 sed]# sed -n '/bus/'Ip test.txt    I忽略大小写，grep -i

222222222.r.olo:ddedBUs

dbus:x:81:81:System message bus:/:/sbin/nologin

删除某些行

[root@lizhipeng01 sed]# sed '1,20'd test.txt     删除1到20行，并没有对test.txt文件做修改，只是不显示1到20行

lizhipeng:x:1000:1000::/home/lizhipeng:/bin/bash

user1:x:1001:1001::/home/user1:/bin/bash

lzp:x:1002:1003::/home/lzp:/bin/bash

user2:x:1003:1006::/home/user2:/bin/bash

user3:x:1004:1005::/home/user3:/bin/bash

user4:x:1006:1005::/home/lizhipeng001:/sbin/nologin

user5:x:1007:1007::/home/user5:/bin/bash

[root@lizhipeng01 sed]# wc -l test.txt

27 test.txt

[root@lizhipeng01 sed]# cp test.txt test.txt.bak      备份

[root@lizhipeng01 sed]# sed -i '1,20'd test.txt      -i ,删除第1到20行，对文件本身有影响

[root@lizhipeng01 sed]# wc -l test.txt

7 test.txt

[root@lizhipeng01 sed]# sed -i '/user2/'d test.txt      删除user2

[root@lizhipeng01 sed]# cat test.txt

lizhipeng:x:1000:1000::/home/lizhipeng:/bin/bash

user1:x:1001:1001::/home/user1:/bin/bash

lzp:x:1002:1003::/home/lzp:/bin/bash

user3:x:1004:1005::/home/user3:/bin/bash

user4:x:1006:1005::/home/lizhipeng001:/sbin/nologin

user5:x:1007:1007::/home/user5:/bin/bash

[root@lizhipeng01 sed]# cp test.txt.bak test.txt

cp：是否覆盖"test.txt"？ y

[root@lizhipeng01 sed]# sed '1,10s/root/toor/g' test.txt      查找替换，1到10行，root替换为toor，对文件本身没有影响

toor:x:0:0:toor:/toor:/bin/bash

[root@lizhipeng01 sed]# sed -r '1,10s/ro+/r/g' test.txt |head

rt:x:0:0:rt:/rt:/bin/bash

bin:x:1:1:bin:/bin:/sbin/nologin

daemon:x:2:2:daemon:/sbin:/sbin/nologin

adm:x:3:4:adm:/var/adm:/sbin/nologin

lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin

sync:x:5:0:sync:/sbin:/bin/sync

shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown

halt:x:7:0:halt:/sbin:/sbin/halt

mail:x:8:12:mail:/var/spool/mail:/sbin/nologin

operator:x:11:0:operator:/rt:/sbin/nologin

[root@lizhipeng01 sed]# head test.txt |sed -r 's/([^:]+):(.*):([^:]+)/\3:\2:\1/'

/bin/bash:x:0:0:root:/root:root

/sbin/nologin:x:1:1:bin:/bin:bin

/sbin/nologin:x:2:2:daemon:/sbin:daemon

/sbin/nologin:x:3:4:adm:/var/adm:adm

/sbin/nologin:x:4:7:lp:/var/spool/lpd:lp

/bin/sync:x:5:0:sync:/sbin:sync

/sbin/shutdown:x:6:0:shutdown:/sbin:shutdown

/sbin/halt:x:7:0:halt:/sbin:halt

/sbin/nologin:x:8:12:mail:/var/spool/mail:mail

/sbin/nologin:x:11:0:operator:/root:operator

[root@lizhipeng01 sed]# head test.txt |sed 's/[a-zA-Z]//g'

::0:0::/://

::1:1::/://

::2:2::/://

::3:4:://://

::4:7::///://

::5:0::/://

::6:0::/://

::7:0::/://

::8:12::///://

::11:0::/://

[root@lizhipeng01 sed]# head test.txt |sed -r 's/(.*)/aaa:&/'    在所有行之前添加aaa:

aaa:root:x:0:0:root:/root:/bin/bash

aaa:bin:x:1:1:bin:/bin:/sbin/nologin

aaa:daemon:x:2:2:daemon:/sbin:/sbin/nologin

aaa:adm:x:3:4:adm:/var/adm:/sbin/nologin

aaa:lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin

aaa:sync:x:5:0:sync:/sbin:/bin/sync

aaa:shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown

aaa:halt:x:7:0:halt:/sbin:/sbin/halt

aaa:mail:x:8:12:mail:/var/spool/mail:/sbin/nologin

aaa:operator:x:11:0:operator:/root:/sbin/nologin