head -n -1 foo.txt > bar.txt
filename="example.txt"
file_size="$(stat --format=%s "$filename")"
trim_count="$(tail -n1 "$filename" | wc -c)"
end_position="$(echo "$file_size - $trim_count" | bc)"
dd if=/dev/null of="$filename" bs=1 seek="$end_position"
dd if=/dev/null of=<filename> bs=1 seek=$(echo $(stat --format=%s <filename> ) - $( tail -n1 <filename> | wc -c) | bc )