De-indent in Bash like Python's textwrap.dedent

dedent.bash

#!/usr/bin/env bash

function dedent() {
  local src min
  src="$(expand -t 2 -)"  # 1 tab = 2 spaces
  if [ -z "$src" ]; then
    echo "dedent: input is empty." >&2
    return 1
  fi
  min="$(
    echo "$src" |
    sed -r 's/^( *).*$/\1/' |
    awk 'BEGIN{m=-log(0)}{m=(a=length)<m ? a : m}END{print m}'
  )"
  if [[ "$min" = "-inf" ]]; then
    echo "dedent: failed to calc min length of \`/^ */'." >&2
    return 1
  fi
  echo "$src" | sed -r 's/^ {'"$min"'}//'
}

function main() {
  dedent <<'A'
  test1
    test2
      test3
                test4
A
}

if [[ "${BASH_SOURCE[0]}" == "${0}" ]]; then
    main "$@"
fi