How can I delete every Xth line in a text file?

Question

Consider a text file with scientific data, e.g.:

5.787037037037037063e-02 2.048402977658663748e-01
1.157407407407407413e-01 4.021264347118673754e-01
1.736111         


        

Answer 1

This might work for you (GNU sed):

seq 10 | sed '0~2d' # delete every 2nd line
1
3
5
7
9
seq 100 | sed '0~10!d' # delete 9 out of 10 lines
10
20
30
40
50
60
70
80
90
100

Answer 2

This is easy to accomplish with awk.

Remove every other line:

awk 'NR % 2 == 0' file > newfile

Remove every 10th line:

awk 'NR % 10 != 0' file > newfile

The NR variable in awk is the line number. Anything outside of { } in awk is a conditional, and the default action is to print.

Answer 3

You could possibly do it with sed, e.g.

sed -n -e 'p;N;d;' file # print every other line, starting with line 1

If you have GNU sed it's pretty easy

sed -n -e '0~10p' file # print every 10th line
sed -n -e '1~2p' file # print every other line starting with line 1
sed -n -e '0~2p' file # print every other line starting with line 2

Answer 4

Try something like:

awk 'NR%3==0{print $0}' file

This will print one line in three. Or:

awk 'NR%10<9{print $0}' file 

will print 9 lines out of ten.

Answer 5

How about perl?

perl -n -e '$.%10==0&&print'       # print every 10th line

Answer 6

You can use a awk and a shell script. Awk can be difficult but...

This will delete specific lines you tell it to:

nawk -f awkfile.awk [filename]

awkfile.awk contents

BEGIN {
if (!lines) lines="3 4 7 8"
n=split(lines, lA, FS)
for(i=1;i<=n;i++)
 linesA[lA[i]]
}
!(FNR in linesA)

Also I can't remember if VIM comes with the standard Ubuntu or not. If not get it.

Then open the file with vim vim [filename]

Then type

:%!awk NR\%2 or :%!awk NR\%2 

This will delete every other line. Just change the 2 to another integer for a different frequency.