Swap two file from one location to another location

swap.sh

#!/bin/sh

if [ $# -ne 2 ] ; then
    echo "usage: $0 source_file target_file" ;
    exit 1 ;
else
    [ -e $1 ] && [ -e $2 ]
    tmp=$(mktemp)
    mv -fv $1 $tmp
    mv -fv $2 $1
    mv -fv $tmp $2
    exit 0 ;
fi