Excuses with Bash

addOneHour.bash

#!/bin/bash

function checkOS {
 ...
}

function addOneHourLinux {
    date -d '+1 hour'
}

function addOneHourMac {
   date -v+1H
}

# set $machine variable
checkOS
# variables are replaced with their values so
# addOneHour$machine on Linux  => addOneHourLinux
# yay for crappy compatibility
addOneHour$machine