arranging the appearance of a text file

Question

I have a text file as shown below

15
5
10
25
35
12

I would like to arrange the above numbers as shown below. How can I do this with awk or sed?

Desired output

15,5,10,25,35,12

Answer 1

Through sed,

$ sed ':a;N;$!ba;s/\n/,/g' file
15,5,10,25,35,12

Through awk,

$ awk -v RS= '{gsub(/\n/,",")}1' file
15,5,10,25,35,12

Answer 2

Here are some versions:

awk '$1=$1' RS=  OFS=, file
15,5,10,25,35,12

paste -d, -s file
15,5,10,25,35,12