Some tips and tricks.

Remove extension from filepath, accounting for:

• Presence of directory slash
• Spaces in filenames and directories
• Removes only one extension for multi-extension files
• Treats dotfiles as regular files
• POSIX-compatible

# Remove extension '$filepath' -> '$stempath'
case "$filepath" in
  */* ) 
    # 'filepath' is a path under some directory
    dirpath="${filepath%/*}"
    filename="${filepath##*/}"
    stem="${filename%.*}"
    test -z "$stem" && stem="$filename"
    stempath="$dirpath/$stem"
    ;;
  *)
    # otherwise, filepath is the filename itself
    stempath="${filepath%.*}"
    test -z "$stempath" && stempath="$filepath"
    ;;
esac

Output

filepath="$1"
...
echo $filepath
echo $stempath
echo

file.tar.gz
file.tar

file.tar
file

file
file

space file.tar.gz
space file.tar

space file.tar
space file

space file
space file

.dotfile.tar
.dotfile

.dotfile
.dotfile

space dir/file.tar.gz
space dir/file.tar

space dir/file.tar
space dir/file

space dir/file
space dir/file

space dir/space file.tar.gz
space dir/space file.tar

space dir/space file.tar
space dir/space file

space dir/space file
space dir/space file

space dir/.dotfile.tar
space dir/.dotfile

space dir/.dotfile
space dir/.dotfile