How can I combine odd and even numbered lines?

here it is, with sed:

sed '$!N;s/\n/,/'

and with awk:

awk '{if (e) {print p","$0;} else {p=$0;} e=!e;}'

awk 'NR%2==0 {print p","$0;} NR%2 {p=$0;}'

This is what the paste command is for. Assume your output is generated with command, then you can do:

$ command | paste -d, - -

or if the output is stored in a file

$ paste -d, - - <file.csv

Example:

paste -d, - - <<END
Line one,csv,csv,csv
Line two,csv,csv
Line three,csv,csv,csv,csv
Line four,csv
END

outputs:

Line one,csv,csv,csv,Line two,csv,csv
Line three,csv,csv,csv,csv,Line four,csv

And another one:

awk -F, ORS=NR%2\?FS:RS infile

You don't need to quote the ? with most shells.

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