Turning multi-line string into single comma-separated

Clean and simple:

awk '{print $2}' file.txt | paste -s -d, -

You can use awk and sed:

awk -vORS=, '{ print $2 }' file.txt | sed 's/,$/\n/'

Or if you want to use a pipe:

echo "data" | awk -vORS=, '{ print $2 }' | sed 's/,$/\n/'

To break it down:

awk is great at handling data broken down into fields
-vORS=, sets the "output record separator" to ,, which is what you wanted
{ print $2 } tells awk to print the second field for every record (line)
file.txt is your filename
sed just gets rid of the trailing , and turns it into a newline (if you want no newline, you can do s/,$//)

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