#!/bin/bash (magic line added for syntax highlighting only)

# Usage: Path_Contains <variable> <path>
# Returns 0 (success) if <path> is a substring of $<variable>
function Path_Contains() {
   local path=":`eval echo '$'$1`:"
   shift
   [ "$path" = "::" ] && return 1  # empty path
   while [ $# -gt 0 ]
   do
      [ "${path##*:$1:*}" ] && return 2  # not found
      shift
   done
}

# Usage: Append_To_Path <variable> <path>
# Add <path> to $<variable> if not already present in its colon-separated
# list of entries. Adds to the end of the list.
function Append_To_Path() {
   local name="$1" term
   shift
   while [ $# -gt 0 ]
   do
      eval term=$1  # tilde expansion
      Path_Contains "$name" "$term" || {
         eval "${name}="'${'"${name}%:"'}'  # remove trailing colon
         eval "${name}=\$${name}:${term}"   # assign
      }
      shift
   done
   eval "${name}="'${'"${name}#:"'}'        # remove starting colon
}

# Usage: Append_To_Path <variable> <path>
# Add <path> to $<variable> if not already present in its colon-separated
# list of entries. Adds to the beginning of the list.
function Prepend_To_Path() {
   local name="$1" term
   shift
   while [ $# -gt 0 ]
   do
      eval term=$1  # tilde expansion
      Path_Contains "$name" "$term" || {
         eval "${name}="'${'"${name}#:"'}'  # remove starting colon
         eval "${name}=${term}:\$${name}"   # assign
      }
      shift
   done
   eval "${name}="'${'"${name}%:"'}'        # remove trailing colon
}