How to delete the line that matches a pattern and the line after it with sed?

Question

I have a file that looks something like:

good text
good text
FLAG bad text
bad text
good text
good text
good test
bad Text FLAG bad text
bad text
good text

I need to delete any line containing "FLAG" and I always need to delete the one line immediately following the "FLAG" line too.

"FLAG" lines come irregularly enough that I can't rely on any sort of line number strategy.

Anyone know how to do this with sed?

Answer 1

Using an extension of the GNU version of sed :

sed -e '/FLAG/,+1 d' infile

It yields:

good text
good text
good text
good text
good test
good text

Answer 2

This works, and doesn't depend on any extensions:

sed '/FLAG/{N
d
}' infile

N reads the next line into the pattern space, then d deletes the pattern space.

Answer 3

Here is one way with awk :

awk '/FLAG/{f=1;next}f{f=0;next}1' file

or

awk '/FLAG/{getline;next}1' file