Bash Script for showing difference between two text files

Question

Lets say I have two lists:

guests-2016.txt:

Peter Michael Frank Dirk 

guests-2017.txt:

Mark Michael Dirk Lilly 

How may I create two new lists of guests

1. Guests that were in guests-2016.txt but are not in guests-2017.txt (former_guests.txt)

2. Guests that were not in guests-2016.txt but are in guests-2017.txt now (new_guests.txt)

Blank lines should be ignored. Only standard utilities should be used.

My idea would be to use diff and do some post processing.

Answer 1

Given two sorted files, comm would do this for you.

See the combinations of the -2 -3 and -1 -3 command line options, for example.

Answer 2

Check, does it do the job. I can add an explanation, if you are needed.

awk ' /^$/{next} FNR == NR {guest_2016[$1] = 1} FNR != NR { if(!guest_2016[$1]) print $1 > "new_guests.txt" delete guest_2016[$1]; } END { for(i in guest_2016) print i > "former_guests.txt" }' guests-2016.txt guests-2017.txt