sed 删除最后几行 和删除指定行

转载原文链接：http://blog.51cto.com/lspgyy/1305489

sed 想删除文件中的指定行，是可以用行号指定也可以用RE来匹配的。

删除指定的行【可以指定行号删除、匹配字符串来删除】

[[email protected] ~]# cat -n seq.txt
     1   ok i will help you
     2   understand sed usage
     3   how to use it
     4   and we should use it in view
     5   now let us
     6   go
     7   hello  my name is
[[email protected] ~]# cat -n seq.txt | sed 3d
     1   ok i will help you
     2   understand sed usage
     4   and we should use it in view
     5   now let us
     6   go
     7   hello  my name is
[[email protected] ~]# cat -n seq.txt | sed /should/d
     1   ok i will help you
     2   understand sed usage
     3   how to use it
     5   now let us
     6   go
     7   hello  my name is
[[email protected] ~]# cat -n seq.txt | sed /ow/d
     1   ok i will help you
     2   understand sed usage
     4   and we should use it in view
     6   go
     7   hello  my name is
[[email protected] ~]# cat -n seq.txt | sed -r /how\|should/d
     1   ok i will help you
     2   understand sed usage
     5   now let us
     6   go
     7   hello  my name is

删除最后几行

[[email protected] ~]# seq 5 > seq01.txt
[[email protected] ~]# cat seq01.txt
1
2
3
4
5
[[email protected] ~]# for((i=1;i<4;i++)); do sed -i ‘$d‘ seq01.txt ; done
#C式for循环
[[email protected] ~]# cat seq01.txt
1
2
[[email protected] ~]# seq 5 > seq01.txt
[[email protected] ~]# cat seq01.txt
1
2
3
4
5
[[email protected] ~]# i=1; while [ $i -le 3 ]; do sed -i ‘$d‘ seq01.txt; ((i++)); done
#while循环
[[email protected] ~]# cat seq01.txt
1
2
[[email protected] ~]# seq 5 > seq01.txt
[[email protected] ~]# cat seq01.txt
1
2
3
4
5
[[email protected] ~]# for i in `seq 3`; do sed -i ‘$d‘ seq01.txt ; done
#bash for循环
[[email protected] ~]# cat seq01.txt
1
2
[[email protected] ~]# seq 5 > seq01.txt
[[email protected] ~]# cat seq01.txt
1
2
3
4
5
#until 循环
[[email protected] ~]# seq 5 > seq01.txt
[[email protected] ~]# cat seq01.txt
1
2
3
4
5
[[email protected] ~]# i=3; until [ $i -le 0 ]; do sed -i ‘$d‘ seq01.txt ; ((i--)); done
[[email protected] ~]# cat seq01.txt
1
2
[[email protected] ~]#

awk练习题

   wang     4
   cui      3
   zhao     4
   liu      3
   liu      3
   chang    5
   li       2

   1 通过第一个域找出字符长度为4的
   2 当第二列值大于3时，创建空白文件，文件名为当前行第一个域$1 (touch $1)
   3 将文档中 liu 字符串替换为 hong
   4 求第二列的和
   5 求第二列的平均值
   6 求第二列中的最大值
   7 将第一列过滤重复后，列出每一项，每一项的出现次数，每一项的大小总和

   1、字符串长度
    awk ‘length($1)=="4"{print $1}‘
   2、执行系统命令
    awk ‘{if($2>3){system ("touch "$1)}}‘
   3、gsub(/r/,"s",域) 在指定域(默认$0)中用s替代r  (sed ‘s///g‘)
    awk ‘{gsub(/liu/,"hong",$1);print $0}‘ a.txt
   4、列求和
    df -h | awk ‘{a+=$2}END{print a}‘
   5、列求平均值
    df -h | awk ‘{a+=$2}END{print a/NR}‘
    df -h | awk ‘{a+=$2;b++}END{print a,a/b}‘ 
   6、列求最大值
    df -h | awk ‘BEGIN{a=0}{if($2>a) a=$2 }END{print a}‘
   7、将第一列过滤重复列出每一项，每一项的出现次数，每一项的大小总和
    awk ‘{a[$1]++;b[$1]+=$2}END{for(i in a){print i,a[i],b[i]}}‘

原文地址：https://www.cnblogs.com/xiaofeng666/p/11234505.html