Search notes:

jq: @csv

@csv formats each incoming arrays as CSV record, thus, it processes a series of arrays, not an array of arrays.

Note the -r (raw output) option in the following example:

$ echo '
  [42, "Hello world"]
  [99, "Ninety nine"]
' |
  jq -r @csv
42,"Hello world"
99,"Ninety nine"