$ cat data
bob,wag,06/13/1958
ashley,hay,01/23/1983
evan,bert,09/11/1972
To output in a file named output-file and display to STDOUT at the same time:
$ awk -v year="$(\date +%Y)" 'BEGIN{FS="/"} {print $0 "," year-$3}' data | tee output-file
bob,wag,06/13/1958,62
ashley,hay,01/23/1983,37
evan,bert,09/11/1972,48
Or to just output to the same file:
$ awk -v year="$(\date +%Y)" 'BEGIN{FS="/"} {print $0 "," year-$3}' data > output-file
