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='2.5.0-dev'

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

# NOTE: $'foo' is the escape sequence syntax of bash
readonly ec=$'\033'      # escape char
readonly eend=$'\033[0m' # escape end
readonly nl=$'\n'        # new line

colorEcho() {
    local color="$1"
    shift
    # check isatty in bash https://stackoverflow.com/questions/10022323
    # if stdout is console, turn on color output.
    [ -t 1 ] && echo "${ec}[1;${color}m$*${eend}" || echo "$*"
}

redEcho() {
    colorEcho 31 "$@"
}

usage() {
    local -r exit_code="${1:-0}"
    (($# > 0)) && shift
    # shellcheck disable=SC2015
    [ "$exit_code" != 0 ] && local -r out=/dev/stderr || local -r out=/dev/stdout

    (($# > 0)) && redEcho "$*$nl" >$out

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

Example:
  ${PROG} arg1 arg2
  ${PROG} */*.py

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

    exit "$exit_code"
}

progVersion() {
    echo "$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 '$1'"
        break
        ;;
    *)
        # if not option, treat all follow files as args
        files=(${files[@]:+"${files[@]}"} "$@")
        break
        ;;
    esac
done

[ "${#files[@]}" -eq 0 ] && {
    redEcho "Error: NO argument!" 1>&2
    exit 1
}

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")"
readonly files relativeTo

for f in "${files[@]}"; do
    ! [ -e "$f" ] && {
        echo "$f does not exists!"
        continue
    }
    realpath "$f" --relative-to="$relativeTo"
done