Sed/Awk to delete first, third, fifth... occurence of new line

hi all im trying to make this

2022-11-14 18:49:59             Indicator is < 3    
1       No
2022-11-14 18:49:59             Indicator is < 10   
1       No
2022-11-14 18:49:59             Indicator is < 22   
1       No
2022-11-14 18:49:59             Indicator is < 1    
1       No

into

2022-11-14 18:49:59             Indicator is < 3    1       No
2022-11-14 18:49:59             Indicator is < 10   1       No
2022-11-14 18:49:59             Indicator is < 22   1       No
2022-11-14 18:49:59             Indicator is < 1    1       No

i found that you can use sed 's/something/some//2' for every second encounter but how to make it for 1st, 3th, 5th,.... and so one

CodePudding user response：

Try this with awk using modulo.

$ awk 'NR % 2 == 0{print prev, $0} {prev = $0}' file
2022-11-14 18:49:59             Indicator is < 3     1       No
2022-11-14 18:49:59             Indicator is < 10    1       No
2022-11-14 18:49:59             Indicator is < 22    1       No
2022-11-14 18:49:59             Indicator is < 1     1       No

It looks at the record number NR and calculates modulo 2 of it. Since every second line comes out as 0 it will then print the previous prev and the current $0 line.