How to remove multiple lines per occurrence in a file?

Question

Say I have this 857835 line file, containing stuff like this:

a1
rubbish1
rubbish2
rubbish3
rubbish4
a1
rubbish5
rubbish6
rubbish7
rubbish8

And I wish to remove all occurences of a1 and the next line (rubbish1 and rubbish5 in this example). How do I do it?

I've tried grep 'a1' -v -A1 to no avail, and my sed skillz are not really great :}

My Google-fu has not been able to help me this time, someone please help!

asoundmove · Accepted Answer · 2011-02-09T21:45:30.723

17

Try:

sed -e '/^a1$/,+1d' "filename"

This means from /^a1$/ to the next line, delete

The ^ and $ ensure you match the whole line, so a hidden a1 will not be matched.

edited Feb 09 '11 at 21:45

answered Feb 09 '11 at 03:13

asoundmove

6

You might want ^ and $ in that match, to force matching whole lines. – Jander Feb 09 '11 at 04:16
@Jander: Sure, corrected – asoundmove Feb 09 '11 at 21:44

score 12 · Answer 2 · answered Feb 09 '11 at 04:21

The following will work on non-GNU sed (the ,+1 address syntax is a GNU extension):

sed -e '/^a1$/,/^/d' my_file >my_filtered_file

"Starting at a line that reads exactly 'a1', and ending at the next line for which the beginning of the line exists (i.e. the next line), delete."

It's much less extensible than @asoundmove's answer, though, as deleting a different number of lines would take an entirely different script.

2 Answers2