Removing leading zeros before passing a shell variable to another command

Question

It turns out that iptables doesn\'t handle leading zeros too well. As $machinenumber that is used has to have a leading zero in it for other purposes, the idea

Answer 1

You don't need to use sed or another external utility. Here are a couple of ways Bash can strip the leading zeros for you.

iptables -t nat -I POSTROUTING -s "10.$machinetype.$((10#$machinenumber)).0/24" -j MASQUERADE

The $(()) sets up an arithmetic context and the 10# converts the number from base 10 to base 10 causing any leading zeros to be dropped.

shopt -s extglob
iptables -t nat -I POSTROUTING -s "10.$machinetype.${machinenumber##+(0)}.0/24" -j MASQUERADE

When extglob is turned on, the parameter expansion shown removes all leading zeros. Unfortunately, if the original value is 0, the result is a null string.