Toss away music that's already converted with iTunes. Flexible, file extension is a variable, locations are variables.

toss_away_converted_music.sh

#!/bin/bash

# CHANGE THESE!!
# This is the folder where your music is located (*all* music within this folder is handled)
DIRECTORY="/path/to/your/music"
# this is the safe (temporary?) location for your files.
NEW_PLACE="/path/to/the/destination/folder"


ORG_EXT='.m4a'
CONVERTED_EXT='.mp3'
# Change this to 1 to get more output.
VERBOSE=0

if [ -z "$todo" ]; then
  todo=0
  conv=0
fi

find $DIRECTORY -type f -name "*$ORG_EXT" | while read FILE; do

  echo "----------------------"
  BASE=$(basename "$FILE" $ORG_EXT)
  if [ "$VERBOSE" != "0" ]; then echo " ..base is '$BASE'"; fi
  SUBDIR=$(dirname "$FILE")
  if [ "$VERBOSE" != "0" ]; then echo " ..SUBdir  is '$SUBDIR'"; fi
  NEWDIR=${SUBDIR/$DIRECTORY/$NEW_PLACE}
  if [ "$VERBOSE" != "0" ]; then echo " ..NEW dir  is '$NEWDIR'"; fi
  echo -n "Processing $FILE ..."
  
  if [ "${BASE:0:1}" != "." ]; then
    if [ "$VERBOSE" != "0" ] && [ -f "$SUBDIR/$BASE$ORG_EXT" ]; then
      echo -n " .... ORG_EXT found"
   fi
   
   if  [ "$VERBOSE" != "0" ] && [ -f "$SUBDIR/$BASE$CONVERTED_EXT" ] ; then
     echo -n ' .... $CONVERTED_EXT found'
    fi
   
    if  [ "$VERBOSE" != "0" ]; then echo " .... lookup for '$SUBDIR/$BASE$CONVERTED_EXT' and '$SUBDIR/$BASE$ORG_EXT' done --- continue." ; fi
   
    if  [ -f "$SUBDIR/$BASE$CONVERTED_EXT" ] && [ -f "$SUBDIR/$BASE$ORG_EXT" ]; then
      if  [ "$VERBOSE" != "0" ]; then echo "VERIFY $NEWDIR ..."; fi
      if [ ! -d "$NEWDIR" ]; then
        echo -n " ... creating dir $NEWDIR"
        mkdir -p "$NEWDIR" && echo ' ...created' || echo ' ...failed!'
      fi
      conv=$(( $conv + 1 ));
      echo -n " ==> Moving $conv... to '$NEWDIR/$BASE$ORG_EXT'"
      mv "$SUBDIR/$BASE.m4a" "$NEWDIR/$BASE$ORG_EXT" && echo " ==> Done." || echo " ==> FAILED!!"
    else
      todo=$(( $todo + 1 ));
      echo " ==> SKIPPING $todo, file not yet converted."
    fi
  else
    echo -n " ==> SKIPPING, filename starts with a dot."
    echo " ==> remove the file"
    rm  "$SUBDIR/$BASE$ORG_EXT"
  fi
done