linux - grep -A <num> untill a string -

assuming have file containing following:

chapter 1 blah blah blah num blah num num blah num blah ... blah num chapter 2 blah blah 

and want grep file take lines chapter 1 blah blah blah num (the line before next chapter).

the things know are

1. the stating string chapter 1 blah blah
2. somewhere after there line starting chapter

a dummy way

grep -a <num> -i "chapter 1" <file> 

with large enough <num> whole chapter in it.

any ideas?

this easy awk

awk '/chapter/ {f=0} /chapter 1/ {f=1} f' file chapter 1 blah blah blah num blah num num blah num blah ... blah num 

it print line if flag f true.
chapter 1 , next chapter changes flag.

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you can use range awk less flexible if have other stuff test.

awk '/chapter 1/,/chapter [^1]/ {if (!/chapter [^1]/) print}' file chapter 1 blah blah blah num blah num num blah num blah ... blah num