#!/bin/sh

# This is designed to be sh, ksh, bash compatible

# ------------------------------------------------------------------------------

buildpath ()
{
  (
    dbg=false
    if [ $# -gt 0 ]; then
      if [ x"$1" = x-d ]; then
        dbg=true
        shift
      fi
    fi
    export dbg

    if [ $# -eq 0 ]; then
      cat 1>&2 <<-EnD
`basename $0` [-d] directory-or-search-path [directory-or-search-path] ...
    -d    Produces debug output on the standard error stream
  Search paths are split at colons into directory path elements; these and
  any plain directory path arguments are read in order, checked to make sure
  the directory exists, and added, at most once, with colon separators, to
  the output. The result is a new colon-separated search-path, written to
  the standard output stream.
EnD

    else
      ( for dp in "$@"; do
          case "$dp" in
            *:*)
              # split args containing colons into lines on stdout
              echo "$dp" | tr : '\n'
              ;;
            *)
              # just output non-colon-containing args one per line
              echo "$dp"
              ;;
          esac
        done
      ) |
      (
        IFS=""                      # do not allow space separators inside lines
        i=0
        while read d; do            # read a line into $d
          case ":${p}:" in
            *:${d}:*)
              # $d has already been seen: ignore duplicate
              $dbg && echo "dupl $d" 1>&2
              ;;
            *)
              if [ -d "$d" ]; then
                # $d is a directory: add it to path $p
                i=`expr $i + 1`
                # or --> i=$(($i + 1))
                $dbg && echo `printf "%4d %s" $i $d` 1>&2
                p="$p$sep$d"
                sep=":"
              else
                # $d is not a directory
                $dbg && echo "!dir $d" 1>&2
              fi
              ;;
          esac
        done
        # all done: echo the new path $p
        echo $p
      )
    fi
  )
}

buildpath "$@"