Common set operations to perform on email lists. Assumes one email per line, and handles case insensitivity.

email-list-set-operations.sh

# Enter two file names as arguments.
# Will print out the ones that appear in both files.
# This is a set intersection.
emails-common-to-both () {
  comm -12 -i  <(sort -u -f "$1") <(sort -u -f "$2");
};

# Enter two filenames.
# Will print emails from first that don't appear in second.
# This is like a set subtraction.
emails-unique-to-first () {
  comm -i -23 <(sort -u -f "$1") <(sort -u -f "$2")
};

# Enter two filenames.
# Creates the union of the two (case insensitive).
emails-combined-from-both () {
  sort -u -f "$1" "$2"
};