Turning multiple lines into one comma separated line

There are many ways it can be achieved. The tool you use mostly depends on your own preference or experience.

Using tr command:

tr '\n' ',' < somefile

Using awk:

awk -F'\n' '{if(NR == 1) {printf $0} else {printf ","$0}}' somefile

Using paste command:

paste -d, -s file

file

aaa
bbb
ccc
ddd

xargs

cat file | xargs

result

aaa bbb ccc ddd 

xargs improoved

cat file | xargs | sed -e 's/ /,/g'

result

aaa,bbb,ccc,ddd 

xargs -a your_file | sed 's/ /,/g'

This is a shorter way.