Replace every n'th occurrence in huge line in a loop

Question

I have this line for example:

1,2,3,4,5,6,7,8,9,10

I want to insert a newline (\\n) every 2nd occurrence of \",\" (replace the 2nd, with ne

Answer 1

I would use awk to do this:

$ awk -F, '{ for (i=1; i<=NF; ++i) printf "%s%s", $i, (i%2?FS:RS) }' file
1,2
3,4
5,6
7,8
9,10

It loops through each field, printing each one followed by either the field separator (defined as a comma) or the record separator (a newline) depending on the value of i%2.

It's slightly longer than the sed versions presented by others, although one nice thing about it is that you can alter the number of columns per line easily by changing the 2 to whatever value you like.

To avoid a trailing comma after the last field in the case where the number of fields isn't evenly divisible, you can change the ternary to i<NF&&i%2?FS:RS.

Answer 2

Can't add comment to wintermutes answer but it doesn't need the first , section as it will have to have had a previous field to be comma separated.

sed 's/\(,[^,]*\),/\1\n/g'

Will work the same

Also I'll add another alternative( albeit worse and leaves a trailing newline)

echo "1,2,3,4,5,6,7,8,9,10" | xargs -d"," -n2 | tr ' ' ','

Answer 3

This might work for you (GNU sed):

sed 's/,/\n/2;P;D' file

Answer 4

If I understand what you're trying to do correctly, then

echo '1,2,3,4,5,6,7,8,9,10' | sed 's/\([^,]*,[^,]*\),/\1\n/g'

seems like the most straightforward way. \([^,]*,[^,]*\) will capture 1,2, 3,4, and so forth, and the commas between them are replaced with newlines through the usual s///g. This will print

1,2
3,4
5,6
7,8
9,10