How to make grep for a regex that appear multiple times in a line

I want to grep a regex. The pattern I am searching for may appear multiple times in a line. If the pattern appeared many times, I want to separate each occurrence by a comma and print **the match only** not the full line in a new file. If it did not appear in a line I want to print **n.a.** Example. I want to use this regex to find numbers in the pattern: [12.123.1.3]. grep -oh "\[\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\]" 'filename' input file (input.txt) blabla [11.335.2.33] xyuoeretrete [43.22.11.88] jfdfjkfbs [55.66.77.88] blabla [66.223.44.33] foo bar blabla [1.2.33.3] xyuoeretrete bla[1.32.2.4] intended result in a new file (output.csv): 11.335.2.33,43.22.11.88,55.66.77.88 66.223.44.33 n.a. 1.2.33.3,1.32.2.4 **Note: I use Ubuntu**