rp

#!/bin/bash
# @Function
# convert to Relative Path.
#
# @Usage
#   # if 1 argument, print relative path to current dir.
#   $ ./rp /etc/apache2/httpd.conf
#   # if more than 1 argument, print relative path to last argument.
#   $ ./rp a.txt ../b.txt /etc/passwd /etc/apache2
#
# @online-doc https://github.com/oldratlee/useful-scripts/blob/dev-2.x/docs/shell.md#-ap-and-rp
# @author Jerry Lee (oldratlee at gmail dot com)
set -eEuo pipefail

# NOTE: DO NOT declare var PROG as readonly in ONE line!
PROG="$(basename -- "$0")"
readonly PROG
readonly PROG_VERSION='2.6.0-dev'

################################################################################
# util functions
################################################################################

colorPrint() {
  local color="$1"
  shift
  # if stdout is a terminal, turn on color output.
  #   '-t' check: is a terminal?
  #   check isatty in bash https://stackoverflow.com/questions/10022323
  if [ -t 1 ]; then
    printf '\e[1;%sm%s\e[0m\n' "$color" "$*"
  else
    printf '%s\n' "$*"
  fi
}

redPrint() {
  colorPrint 31 "$@"
}

die() {
  redPrint "Error: $*" >&2
  exit 1
}

portableRelPath() {
  local file="$1" relTo="$2" uname

  uname="$(uname)"
  case "$uname" in
  Linux* | CYGWIN* | MINGW*)
    realpath "$f" --relative-to="$relTo"
    ;;
  Darwin*)
    local py_args=(-c 'import os, sys; print(os.path.relpath(sys.argv[1], sys.argv[2]))' "$file" "$relTo")
    if command -v grealpath >/dev/null; then
      grealpath "$f" --relative-to="$relTo"
    elif command -v python3 >/dev/null; then
      python3 "${py_args[@]}"
    elif command -v python >/dev/null; then
      python "${py_args[@]}"
    else
      die "fail to find command(grealpath/python3/python) to get relative path!"
    fi
    ;;
  *)
    die "NOT support uname($uname)!"
    ;;
  esac
}

usage() {
  local -r exit_code="${1:-0}"
  (($# > 0)) && shift
  local -r out=$(((exit_code != 0) + 1))

  # NOTE: $'foo' is the escape sequence syntax of bash
  local nl=$'\n' # new line
  (($# > 0)) && redPrint "$*$nl" >&"$out"

  cat >&"$out" <<EOF
Usage: ${PROG} [OPTION]... [FILE]...
convert to Relative Path.

Example:
  ${PROG} path    # relative to current dir
  ${PROG} path1 relativeToPath
  ${PROG} */*.c relativeToPath

Options:
  -h, --help      display this help and exit
  -V, --version   display version information and exit
EOF

  exit "$exit_code"
}

progVersion() {
  printf '%s\n' "$PROG $PROG_VERSION"
  exit
}

################################################################################
# parse options
################################################################################

declare -a files=()
while [ $# -gt 0 ]; do
  case "$1" in
  -h | --help)
    usage
    ;;
  -V | --version)
    progVersion
    ;;
  --)
    shift
    files=(${files[@]:+"${files[@]}"} "$@")
    break
    ;;
  -*)
    usage 2 "${PROG}: unrecognized option '$1'"
    ;;
  *)
    # if not option, treat all follow files as args
    files=(${files[@]:+"${files[@]}"} "$@")
    break
    ;;
  esac
done

[ "${#files[@]}" -eq 0 ] && die "NO argument!"

if [ "${#files[@]}" -eq 1 ]; then
  relativeTo=.
else
  argc="${#files[@]}"

  # Get last argument
  relativeTo="${files[argc - 1]}"
  files=("${files[@]:0:argc-1}")
fi

[ -f "$relativeTo" ] && relativeTo="$(dirname -- "$relativeTo")"
[ -e "$relativeTo" ] || die "relativeTo dir($relativeTo) does NOT exists!"

readonly files relativeTo

################################################################################
# biz logic
################################################################################

has_error=false

for f in "${files[@]}"; do
  if [ -e "$f" ]; then
    portableRelPath "$f" "$relativeTo"
  else
    redPrint "error: $f does not exists!" >&2
    has_error=true
  fi
done

# set exit status
! $has_error