move the last line of a file to the beginning IN PLACE

flop.sh

#!/usr/bin/env bash

file=$1
last=$(tail -n 1 $file)
# if you do this in a chmoded file you have to double the backslash as I have in the next line
sed -i -e '$d' -e "1 i\\
$last
" $file

# NOTE: for BSD sed (non-gnu, aka: OSX), use: -i ''

flop2.sh

#!/usr/bin/env bash

file=$1

ed $file <<EOF
\$m0
w
q
EOF