# IP address string manipulation problem

I am trying to build three octets `10.AB.C9`

from a 5 digit number: `12ABC`

:

`12`

= first octet`AB`

= Second octet`C`

= Third octet

There are two scenarios with my existing code that can cause an in correct IP to generate.

If C has a leading zero for example: 02 then the third octet will 027 and IPs can’t have hardcoded leading zeros.

```
five_digits=12620
if [ "${five_digits:4:1}" -eq 0 ]; then
ip_main="10.${five_digits:2:2}.9"
gateway_ip_prefix="10.${five_digits:2:2}.2"
elif [ "${five_digits:4:1}" -ne 0 ]; then
ip_main="10.${five_digits:2:2}.${five_digits:4:1}9"
gateway_ip_prefix="10.${five_digits:2:2}.${five_digits:4:1}2"
```

The above code solves the leading zero problem in C

The second scenario is where A is zero meaning the second octet will have a leading zero. I am not sure how to handle that scenario and hopefully make the script simpler.

I would break each octet apart, and remove any leading zeroes from each, then concatenate them together. Something like this:

```
str="$five_digits"
if [[ ${#str} != 5 ]] || [[ ${str:0:2} != "12" ]]; then
echo invalid input >&2;
exit 1;
fi
a=10 # first octet, constant
b=${str:2:2} # second octet
b=${b#0} # remove one leading zero
c=${str:4:1}9 # third octet
c=${c#0} # remove one leading zero
res="$a.$b.$c" # concatenated result
echo "$res"
```

E.g. that turns the input string `12345`

to `10.34.59`

; `12055`

to `10.5.59`

; and `12000`

to `10.0.9`

.