Today I realised, that ash of Red Hat Linux SuX0r more than I could expect: 

This works fine in my Debian GNU/Linux 2.2 (Potato): 

#!/bin/ash

BEATHOUR=$(date -u +%H)

BEATHOUR=$(( ${BEATHOUR} + 1 ))


But In Red Hat Linux 6.2 I needed to hack it like this: 


#!/bin/ash

BEATHOUR=$(date -u +%k | sed 's/\ //')

if test "${BEATHOUR}" = "0"
then
 BEATHOUR=1
else
 BEATHOUR=$((${BEATHOUR}+1))
fi