Add no-clobber option to CLI

So the user can abort if the target directory would be overwritten.

Pork:  Remove trailing whitespace

AAXtoMP3

@@ -5,7 +5,7 @@
 # Command Line Options
 
 # Usage Synopsis.
-usage=$'\nUsage: AAXtoMP3 [--flac] [--aac] [--opus ] [--single] [--chaptered]\n[-e:mp3] [-e:m4a] [-e:m4b] [--authcode <AUTHCODE>]\n[--target_dir <PATH>] [--complete_dir <PATH>] [--validate]\n{FILES}\n'
+usage=$'\nUsage: AAXtoMP3 [--flac] [--aac] [--opus ] [--single] [--chaptered]\n[-e:mp3] [-e:m4a] [-e:m4b] [--authcode <AUTHCODE>] [--no-clobber]\n[--target_dir <PATH>] [--complete_dir <PATH>] [--validate]\n{FILES}\n'
 codec=libmp3lame            # Default encoder.
 extension=mp3               # Default encoder extention.
 mode=chaptered              # Multi file output
@@ -45,6 +45,8 @@ while true; do
     -C | --complete_dir ) completedir="$2";                                             shift 2 ;;
                       # Authorization code associate with the AAX file(s)
     -A | --authcode   ) auth_code="$2";                                                 shift 2 ;;
+                      # Don't overwrite the target directory if it already exists
+    -n | --no-clobber ) noclobber=1;                                                    shift ;;
                       # Extremely verbose output.
     -d | --debug      ) DEBUG=1;                                                        shift ;;
                       # Validate ONLY the aax file(s) No transcoding occurs
@@ -234,7 +236,7 @@ if [[ "x${targetdir}" != "x"  ]]; then
 fi
 
 # -----
-# Check the target dir for if set if it is writable
+# Check the completed dir for if set if it is writable
 if [[ "x${completedir}" != "x"  ]]; then
   if [[ ! -w "${completedir}" || ! -d "${completedir}" ]] ; then
     echo "ERROR Complete Directory does not exist or is not writable: \"$completedir\""
@@ -283,7 +285,7 @@ validate_aax() {
     log "Test 2 SUCCESS: ${media_file}"
   fi
 
-  # This is a big test only performed when the --validate swicth is passed.
+  # This is a big test only performed when the --validate switch is passed.
   if [[ "${VALIDATE}" == "1" ]]; then
     output="$(ffmpeg -hide_banner -activation_bytes ${auth_code} -i "${media_file}" -vn -f null - 2>&1)"
     if [[ $? != "0" ]] ; then
@@ -360,6 +362,10 @@ do
   album_date="$(get_metadata_value date)"
   copyright="$(get_metadata_value copyright)"
 
+  if [[ "${noclobber}" = "1" ]] && [[ -d "${output_directory}" ]]; then
+    log "Noclobber enabled but directory '${output_directory}' exists. Exiting to avoid overwriting"
+    exit 0
+  fi
   mkdir -p "${output_directory}"
 
   # Fancy declaration of which book we are decoding.  Including the AUTHCODE.

README.md

@@ -29,7 +29,7 @@ Thanks to kbabioch, this script has also been packaged in the [AUR](https://aur.
 
 ## Usage(s)
 ```
-bash AAXtoMP3 [-f|--flac] [-o|--opus] [-a|-aac] [-s|--single] [-c|--chaptered] [-e:mp3] [-e:m4a] [-e:m4b] [-A|--authcode <AUTHCODE>] [-t|--target_dir <PATH>] [-C|--complete_dir <PATH>] [-V|--validate] [-d|--debug] [-h|--help] <AAX INPUT_FILES>...
+bash AAXtoMP3 [-f|--flac] [-o|--opus] [-a|-aac] [-s|--single] [-c|--chaptered] [-e:mp3] [-e:m4a] [-e:m4b] [-A|--authcode <AUTHCODE>] [-n|--no-clobber] [-t|--target_dir <PATH>] [-C|--complete_dir <PATH>] [-V|--validate] [-d|--debug] [-h|--help] <AAX INPUT_FILES>...
 ```
 
 * **&lt;AAX INPUT_FILES&gt;**... are considered input file(s), useful for batching!
@@ -39,6 +39,7 @@ bash AAXtoMP3 [-f|--flac] [-o|--opus] [-a|-aac] [-s|--single] [-c|--chaptered] [
 * **-o** or **--opus**   Ogg/Opus Encoding defaults to multiple file output by chapter. The extention is .ogg
 * **-a** or **--aac**    AAC Encoding and produce a m4a single files output.
 * **-A** or **--authcode &lt;AUTHCODE&gt;** for this execution of the command use the provided &lt;AUTHCODE&gt; to decode the AAX file.
+* **-n** or **--no-clobber** If set and the target directory already exists, AAXtoMP3 will exit without overwriting anything.
 * **-t** or **--target_dir &lt;PATH&gt;** change the default output location to the named &lt;PATH&gt;. Note the default location is ./Audiobook of the directory to which each AAX file resides.
 * **-C** or **--complete_dir &lt;PATH&gt;** a directory to place aax files after they have been decoded successfully. Note make a back up of your aax files prior to using this option. Just in case something goes wrong.
 * **-V** or **--validate** Perform 2 validation tests on the supplied aax files. This is more extensive than the normal validation as we attempt to transcode the aax file to a null file.  This can take a long period of time. However it is useful when inspecting a large set of aax files prior to transcoding. As download errors are common with Audible servers.