Get the directory of a path. Example use is to get a bash script's location for loading other bash scripts as modules.

mydir.bash

#!/usr/bin/env bash

# Prints error messages to stderr
#   @PARAM Concatenates parameters with IFS (default space) to form an error
# message.
#   @OUT Prints error message preceeded by "ERROR: " to standard error,
# translating escapes.
#   @REQUIRES: echo -e
function sayErr() {
   echo -e "ERROR: $@" >&2
}

# Figure out the directory this script is in and return it as $__
#   @PARAM $1 - path to obtain directory to. May be absolute or relative
# and may be or contain links
#   @RET directory of "$1" as absolute path, in $__. May contain or be a link.
#   @IO Error 1 if $1 path does not exist
#   @IO Error 1 if $1 path is a link but can not be resolved due to a missing
# target or cyclical links.
#   @REQUIRES: readlink, cd -P, dirname, pwd
function getMyDir() {
   
   local path="$1"
   if [[ ! -e $path && ! -L $path ]]; then
      sayErr "Does not exist: \"$path\"."
      return 1
   fi
   
   # Resolve source path that is (ends in) in a symlink. Not using
   # readlink -f as that does not work on macs. Don't care about links in path
   local count=1000
   local realPath="$path"
   while [[ -L "$realPath" && $count -gt 0 ]]; do
      # Handle relative paths to link, need to resolve in context.
      if [[ $realPath != /* ]]; then
         local dir="$( dirname "$realPath" )"
         realPath="$dir/$realPath"
      fi
      realPath="$(readlink "$realPath")"
      (( count-=1 ))
   done
   if [[ ! -e $realPath ]]; then
      sayErr "Path \"$path\" resolves to missing link: \"$realPath\"."
      return 1
   fi
   if [[ $count == 0 ]]; then
      sayErr "Too many links, probably cyclical. Can't resolve \"$path\"."
      return 1
   fi
   
   # Resolve relative path and return.
   # With IO capture, > dev/null needed to dump possible unwanted output. 
   __="$( cd -P "$( dirname "$SOURCE" )" >/dev/null 2>&1 && pwd )"
}

# Main entry point; called if executed
function main() {
   getMyDir "$BASH_SOURCE" || exit $!
   echo "$__"
}

# If this script is sourced, don't run main.
# Nothing should follow this, the exit status of main should
# be the exit status of the script.
[[ "$0" == "$BASH_SOURCE" ]] && main "$@"