sed to delete the last few lines and delete the specified line

Reproduced original link: http://blog.51cto.com/lspgyy/1305489

sed want to delete files in the specified line, is used to specify the line number can also be used to match the RE.

Delete the specified line [can specify the line number to delete, delete the matching string]

[root@Jason64-17 ~]# 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
[root@Jason64-17 ~]# 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
[root@Jason64-17 ~]# 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
[root@Jason64-17 ~]# 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
[root@Jason64-17 ~]# 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

Delete the last few lines

[root@Jason64-17 ~]# seq 5 > seq01.txt                                      
[root@Jason64-17 ~]# cat seq01.txt
1
2
3
4
5
[root@Jason64-17 ~]# for((i=1;i<4;i++)); do sed -i '$d' seq01.txt ; done  
#C式for循环 
[root@Jason64-17 ~]# cat seq01.txt
1
2
[root@Jason64-17 ~]# seq 5 > seq01.txt
[root@Jason64-17 ~]# cat seq01.txt    
1
2
3
4
5
[root@Jason64-17 ~]# i=1; while [ $i -le 3 ]; do sed -i '$d' seq01.txt; ((i++)); done
#while循环  
[root@Jason64-17 ~]# cat seq01.txt
1
2
[root@Jason64-17 ~]# seq 5 > seq01.txt
[root@Jason64-17 ~]# cat seq01.txt
1
2
3
4
5
[root@Jason64-17 ~]# for i in `seq 3`; do sed -i '$d' seq01.txt ; done
#bash for循环
[root@Jason64-17 ~]# cat seq01.txt    
1
2
[root@Jason64-17 ~]# seq 5 > seq01.txt
[root@Jason64-17 ~]# cat seq01.txt    
1
2
3
4
5
#until 循环
[root@Jason64-17 ~]# seq 5 > seq01.txt
[root@Jason64-17 ~]# cat seq01.txt    
1
2
3
4
5
[root@Jason64-17 ~]# i=3; until [ $i -le 0 ]; do sed -i '$d' seq01.txt ; ((i--)); done
[root@Jason64-17 ~]# cat seq01.txt
1
2
[root@Jason64-17 ~]#

awk exercises

   . 4 Wang
   CUI. 3
   Zhao. 4
   Liu. 3
   Liu. 3
   Chang. 5
   Li 2

   1 identify the character length of the first field 4 by
   2 when the second column value is greater than 3, create a blank file named line current domain $ 1 (Touch $ 1)
   3 in the document string with liu Hong
   . 4 of the second column and seeking
   the average of the second column is seeking 5
   6 selecting the maximum value in the second column
   after the first column of the filter 7 is repeated, each of the lists, the number of occurrences of each item, each the sum of the sizes

   1, a string
    awk 'length ($ 1) == ". 4" {Print $ 1}'
   2, execution system
    awk '{IF ($ 2>. 3) {System ( "Touch" $ 1)}}'
   . 3, gsub ( / r /, "s", domain) in the specified domain (default $ 0) with s an alternative R & lt (Sed 's /// G')
    awk '{gsub (/ Liu /, "Hong", $. 1); Print $ 0 } 'a.txt
   . 4, column summation
    DF -H | awk' $ {2} = A + Print the END {A} '
   . 5, the column averaging
    df -h | awk' {a + = $ 2} END {print a / NR } '
    DF -H | awk' {A + = $ 2; B ++} the END {Print A, A / B} '
   . 6, column selecting the maximum value
    df -h | awk' BEGIN {a = 0} {if ($ 2> a) the END = $ 2} a {a} Print '
   . 7, each of the filters listed in the first column is repeated the number of times each occurrence, each of the total size
    awk' {a [$ 1] ++; b [$ 1 ] + = $ 2} END { for (i in a) {print i, a [i], b [i]}} '

sed to delete the last few lines to delete the specified line and use awk

sed to delete the last few lines and delete the specified line

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