sed match pattern N times

Question

I want to split a file into chunks with 2 words each.

$cat tmp
word1 word2 word3 word4 word5 word6 word7
$sed -e 's/word. word. /&\n/g' tmp
word1 word2 
word3 word4 
word5 word6 
word7
$sed -e 's/word. \{2\}/&\n/g' tmp
word1 word2 word3 word4 word5 word6 word7

I expected the last command to give same result as the one before it. What is wrong?

Answer 1

Sorry, seems like I figured it out just after posting.

It needs to be

sed -e 's/\(word. \)\{2\}/&\n/g' tmp

Apparently the parentheses are needed to let sed apply {2} condition on the entire pattern word. and not just preceding space.

Answer 2

Another way in sed:

$ sed 's/ /\x1&\x2/g; s/\([^\x1]*[\x1][^\x2]*[\x2][^\x1]*\)[\x1][^\x2]*[\x2]/\1\
/g; s/[\x1\x2]//g'

Answer 3

For the general case of matching N times:

$ perl -ple '$N=3;s/(\S+ ){$N}\K/\n/g' tmp
word1 word2 word3 
word4 word5 word6 
word7