pathto

#!/usr/bin/env ruby -w
#  Copyright 2014 Noel Cower
#
#  Licensed under the Apache License, Version 2.0 (the "License");
#  you may not use this file except in compliance with the License.
#  You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
#  Unless required by applicable law or agreed to in writing, software
#  distributed under the License is distributed on an "AS IS" BASIS,
#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#  See the License for the specific language governing permissions and
#  limitations under the License.
#
#  -----------------------------------------------------------------------------
#
#  pathto [-z] [--relative|--absolute|--base=BASE|--no-base] path [...]

require 'pathname'
require 'stringio'

def out_io
  $stdout.tty? ? $stdout : $stderr
end

def emit_license
  out_io.puts <<-LICENSESTR.gsub(/^ {4}/, '')
    Copyright 2014 Noel Cower

    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
    You may obtain a copy of the License at

         http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
  LICENSESTR

  exit 0
end

def emit_help(short = false)
  out_io.puts <<-HELPSTR.gsub(/^ {4}|^ +$/, '').chomp
    pathto [-z] [--relative|--absolute|--base=BASE|--no-base] path [...]
#{ (short ? <<-SHORTHELP : <<-LONGHELP).chomp }

      -z      Emits paths separated by null characters. Must come first.
      -a      Emits absolute paths.
      -r      Emits relative paths
      -bBASE  Sets the base path to BASE.
      -p      Sets the base path to the pwd.
      -h      Displays longer help text.
      -l      Displays the script's license header.

  SHORTHELP

    Emits any number of relative or absolute paths relative to the given
    base path. If no base path is given, defaults to the pwd.

      -z
        If specified, pathto emits paths separated by null characters.
        This must be the first argument to pathto as it affects all output.

      --absolute | -a
        Next path is emitted as an absolute path. This converts relative
        paths to absolute paths. By default, emitted paths are absolute.

      --relative | -r
        Next path is emitted as a relative path. This converts absolute
        paths to relative paths.

      --base=BASE | -bBASE
        The next relative path is emitted relative to this base, if either
        --relative is specified or the path is relative. Otherwise, the
        path is echoed as it was input. If BASE is relative, it is expanded
        relative to the pwd.

      --no-base | -p
        Sets the current base path to the pwd.

      --help | -h
        Displays this help text.

      --license | -l
        Displays the license header for this script.

    LONGHELP
  HELPSTR

  exit 0
end

PWD      = Dir.pwd.freeze
relative = false
base     = PWD

def expand(p)
  File.expand_path(p, PWD)
end

rsep = $\ || "\n"
if ARGV.first == '-z'
  ARGV.shift
  rsep = "\0"
end

outs = []

ARGV.each do |path|
  if base == :swallow
    base = expand(path)
    next
  end

  case path
  when '-r', '--relative'     then relative = true;   next
  when '-a', '--absolute'     then relative = false;  next
  when /^(?:-b|--base=)(.+)$/ then base = expand($1); next
  when '-b', '--base'         then base = :swallow;   next
  when '-p', '--no-base'      then base = PWD;        next
  when '-h', '--help'         then emit_help(false)
  when '-l', '--license'      then emit_license
  end

  abs_path = File.expand_path(path, base)

  if relative
    rel_path = Pathname.new(abs_path).relative_path_from(Pathname.new(base))
    outs << rel_path.to_s
  else
    outs << abs_path
  end
end

emit_help(true) if outs.empty?

$stdout.write outs.join(rsep)