missinglines.bash

#!/usr/bin/env bash

# Installation:
# - Download this file.
# - Name it `missinglines`.
# - Make it executable (`chmod +x missinglines`).
# - Move it to your PATH.

set -o errexit

print_usage() {
  echo "${1}missinglines <file1> <file2>" >&2
  echo "${1}Print lines from file1 which are not in file2." >&2
}

if [[ $* == *'--help'* ]]; then
  print_usage
  exit
fi

if [[ $# != 2 ]]; then
  echo "Expected two arguments:" >&2
  print_usage '  '
  exit 64
fi

file1="$1"
file2="$2"

if [[ ! -f $file1 ]]; then
  echo "Cannot read '$file1'." >&2
  print_usage '  '
  exit 64
fi

if [[ ! -f $file2 ]]; then
  echo "Cannot read '$file2'." >&2
  print_usage '  '
  exit 64
fi

file1_is_copied=nope
file2_is_copied=nope

file1_is_sorted=yep
sort -C "$file1" || file1_is_sorted=nope

file2_is_sorted=yep
sort -C "$file2" || file2_is_sorted=nope

sort_to_tempfile() {
  local tmpfile="$(mktemp missinglines_XXXXXXXXXX)"
  cat "$1" | sort > "$tmpfile"
  echo "$tmpfile"
}

if [[ $file1_is_sorted == nope ]]; then
  file1="$(sort_to_tempfile "$file1")"
  file1_is_copied=yep
fi

if [[ $file2_is_sorted == nope ]]; then
  file2="$(sort_to_tempfile "$file2")"
  file2_is_copied=yep
fi

comm -23 "$file1" "$file2"

if [[ $file1_is_copied == yep ]]; then
  rm "$file1"
fi

if [[ $file2_is_copied == yep ]]; then
  rm "$file2"
fi