CODEWITHSUNDEEP
sed
user2808302
user2808302

Reputation:

Removing chunks of lines with sed

I am trying to go through a file and keep a consecutive group of 4 rows out of each consecutive group of 40 rows.

So in the whole file, I would keep rows 1-4, 41-44, 81-84, etc.
I tried using sed, but I am really only able to remove specific rows, not do a pattern like this.

Many thanks...

Upvotes: 1

Views: 124

Answers (4)

NeronLeVelu
NeronLeVelu

Reputation: 10039

simple but do what is asked (thks to @Jotne for remark based on seq test)

sed -n 'N;N;N;p;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N;N' YourFile

just for fun

sed -n '
x    
s/^$/ppppfffffffffffffffffffffffffffffffffff/
s/^p//
t keep
s/^f//
x
b
:keep
x
p' YourFile

there is another more traditionnal way by using only d, p and N but not funny at all :-). I use a kind of template counter that print and forget lines (the ppppfffffffffffffffffffffffffffffffffff) keep in hold buffer

Upvotes: 0

potong
potong

Reputation: 58430

This might work for you (GNU sed):

sed -n '1~40,+3p' file

Use a 40 line step starting at line 1 and range it over 4 lines.

Upvotes: 2

Jotne
Jotne

Reputation: 41456

This awk should do:

awk 'NR%40==1 || NR%40==2 || NR%40==3 || NR%40==4' file

A loop version:

awk '{for (i=1;i<5;i++) if (NR%40==i) print $0}' file

Found this should work after I tested various solution:

awk 'NR%40~/^[1-4]$/' file

test

seq 1 100 > file


awk 'NR%40~/^[1-4]$/' file
1
2
3
4
41
42
43
44
81
82
83
84

Upvotes: 4

merlin2011
merlin2011

Reputation: 75565

You might be better off with awk. This is not the most concise solution, but should get you what you want. The variable NR represents the row number.

 awk '(NR - 1) % 40 ==0 || (NR - 2) % 40 ==0 || (NR - 3) % 40 ==0 || (NR - 4) % 40 ==0 ' Input.txt

I tested this like this:

 seq 1 50 > /tmp/Input.txt
 awk '(NR - 1) % 40 ==0 || (NR - 2) % 40 ==0 || (NR - 3) % 40 ==0 || (NR - 4) % 40 ==0 ' /tmp/Input.txt

If you want to modify the original file, then output it to a temporary file and move it back.

awk '(NR - 1) % 40 ==0 || (NR - 2) % 40 ==0 || (NR - 3) % 40 ==0 || (NR - 4) % 40 ==0 ' Input.txt > /tmp/TempOutput
mv /tmp/TempOutput Input.txt

Upvotes: 1

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