bash regex

regex_demo_sippet.sh

# INSTANCE_RAM examples
# INSTANCE_RAM=8G or INSTANCE_RAM=12m

regex='^([[:digit:]]+)([GgMm])$'
if [[ "${INSTANCE_RAM}" =~ $regex ]]; then
        num=${BASH_REMATCH[1]}
        unit=${BASH_REMATCH[2]}
        if [[ $unit =~ [Gg] ]]; then
                ((num = num * 1024)) # enables math to work out for odd gigs
        fi
        if [[ $num -lt 512 ]]; then
                echo "INSTANCE_RAM set to ${INSTANCE_RAM} but must be at least 512M"
                exit 1
        fi
fi