Ensure that a file has one and only one final new line

fix-eof.bash

fix_eof() {
  for f; do
    : Add a final new line if needed.
    [ "$(tail -c1 $f)" = "" ] || echo >> $f

    : Remove extra final new lines.
    while [ "$(tail -c2 $f)" = "" ] && [ $(wc -l < $f) -gt 1 ]; do
      sed -i '' '$ d' $f
    done
  done
}

: Fix EOF of all non-binary tracked files.
fix_eof $(git grep --cached --name-only -I '')

fix-eof:test.bash

fix_eof() {
  for f; do
    : Add a final new line if needed.
    [ "$(tail -c1 $f)" = "" ] || echo >> $f

    : Remove extra final new lines.
    while [ "$(tail -c2 $f)" = "" ] && [ $(wc -l < $f) -gt 1 ]; do
      sed -i '' '$ d' $f
    done
  done
}

test() {
  f=$(mktemp)
  printf "$1" > $f
  fix_eof $f
  d=$(diff $f <(printf "$2"))
  [ -z "$d" ] && echo OK || echo -e "Failure:\n$f"
  rm $f
}

test '' ''
test '\n' '\n'
test '\n\n' '\n'
test 'foo' 'foo\n'
test 'foo\n' 'foo\n'
test 'foo\nbar' 'foo\nbar\n'
test 'foo\nbar\n\n' 'foo\nbar\n'