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How can I delete every third AND fourth line in a file?

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Top Forums Shell Programming and Scripting How can I delete every third AND fourth line in a file?
# 1  
Old 12-07-2010
How can I delete every third AND fourth line in a file?
cat test.nmea|awk 'NR%3!=0'

This deletes the 3rd line, or I can delete the fourth but I can't figure out how to delete the 3rd and 4th together. I'm looking for a quick way to make a GPS log half its size.

Also how do I pipe the output to another file?

Hope someone can help!
# 2  
Old 12-07-2010
that is a strange way to truncate a log file but if you must this should work... no need for cat.

Code:
awk 'NR%3!=0 && NR%4!=0' test.nmea >new.file

# 3  
Old 12-07-2010
frank_rizzo's solution deletes lines 3,4,6,8,9,12,15,16 (any line divisible by 3 or 4)

If you want to delete 3,4,7,8,11,12,15,16 (line 3 & 4 out of every group of 4) then you want:

Code:
awk 'NR%4==1 || NR%4==2' test.nmea > new.file

# 4  
Old 12-07-2010
Code:
perl -i -pe 's/.*\s*$// if ($.%3==0 || $.%4==0);' infile

Last edited by k_manimuthu; 12-07-2010 at 11:57 PM.. Reason: format
# 5  
Old 12-08-2010
With Gnu sed:
Code:
sed '3~4d;4~4d'

or
Code:
sed '3~4,4~4d'

I think Chuble_XL is right in interpreting OP's intention.
# 6  
Old 12-08-2010
Code:
awk 'p=!p;{getline}p' infile

Code:
sed -n 'p;n;p;n;n' infile

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