Rename all files in a directory to its lowercase equivalent, skip if a duplicate filename already exists

lowercase-rename.sh

#!/usr/bin/env bash

# Just comment this out to run the script within the target directory.
cd /mnt/example || exit 1

for f in *; do
  lower="$(echo "$f" | tr '[:upper:]' '[:lower:]')"
  
  if [[ "$f" != "$lower" ]]; then
    if [[ -e "$lower" ]]; then
      echo "Skipping '$f': '$lower' already exists."
    else
      mv -- "$f" "$lower"
    fi
  fi
done