Comment by jph

I like shell set operations scripts, because they are quick and easy.

I prefer `awk` over `uniq` and `comm` because awk tends to be faster at set ops that can skip sorting and deduplicating.

Here's my script for union, intersection, etc. See README on GitHub. Suggestions welcome.

https://github.com/sixarm/setop

    #!/bin/sh
    set -eu
    op="$1"; shift

    case  $op  in
      ∪|u|union|or|∨|add|addition|'+'|'|')
        awk '!seen[$0] {print} {seen[$0]=1}' "$@"
        ;;
      ∩|i|intersection|and|∧|'&')
        awk 'FNR==1{argind+=1} seen[$0]+=1 {next} END { for (key in seen) { if (seen[key]==argind) { print key } } }' "$@"
        ;;
      ⊖|d|diff|difference|xor|⊻)
        awk 'FNR==1{argind+=1} seen[$0]+=1 {next} END { for (key in seen) { if (seen[key]==1) { print key } } }' "$@"
        ;;
      ex|except|exclude|subtract|subtraction|'-')
        awk 'NR==FNR{seen[$0]=1;next} seen[$0]=0; END { for (key in seen) { if (seen[key]) { print key } } }' "$@"
        ;;
      extra)
        awk 'BEGIN{argindmax=ARGC-1} FNR==1{argind+=1} argind<argindmax {seen[$0]; next}!($0 in seen)' "$@"
        ;;
      disjoint|n|not|none)
        awk 'seen[$0]==1 {x=1;exit} {seen[$0]=1} END { print x ? "FALSE" : "TRUE"}; exit !!x}' "$@"
        ;;
      *)
    esac