Append to same line in Bash

Question

The file letters.csv contains:

b,a,c,

The file numbers.csv contains:

32
34
25
13

I would like to append numbe

Answer 1

You can do it with paste alone.

First, convert contents in numbers.csv to comma-separated values. -s is the serial option and -d, specifies comma as delimiter:

$ paste -sd, numbers.csv
32,34,25,13

Then append this output to letters.csv by specifying an empty delimiter and process substitution:

$ # use -d'\0' for non-GNU version of paste
$ paste -d '' letters.csv <(paste -sd, numbers.csv) > tmp && mv tmp letters.csv
$ cat letters.csv
b,a,c,32,34,25,13

To modify sed command posted in OP, use command substitution:

$ sed -i -e "s/$/$(sed -e :a -e '{N; s/\n/,/g; ta}' numbers.csv)/" letters.csv
$ cat letters.csv
b,a,c,32,34,25,13