#!/bin/bash
HOST="email.com:1234"
USER="username"
PASS="password"
LCD="/path/to/local/dir"
RCD="/path/to/remote/dir"

if [ ! -e "/tmp/xfer" ]
then
        touch /tmp/xfer

        lftp -c "set ftp:list-options -a;
        open ftp://$USER:$PASS@$HOST;
        lcd $LCD;
        cd $RCD;
        mirror --delete \
                                 --only-missing \
                                 --verbose"

        rm /tmp/xfer
else
        echo "Xfering already going"
fi