Using sed to fill blanks with 0's (zero's) - linux

Question

Does anyone know of a way to replace blanks with 0's? Here's what im trying to do...
Basically i have a script that pulls an ip address and manipulates the address to make a port number out of it.
192.168.202.3 = Port 23
what i need is a smart enough sed command to add 2 0's in front of the 3 making it a full value.
192.168.202.3 = Port 2003
or:
192.168.202.003 = Port 2003
The catch is, if the number already exists then i dont want it to add 0's..
192.168.202.254 = Port 2254
instead of:
192.168.202.254 = Port 200254
Any ideas on how to do it?
Relevant Portion of the script:
# Retrieve local-ipv4 address from meta-data
GET http://169.254.169.254/latest/meta-data/local-ipv4 > /metadata
# Create a manipulated version of ipv4 to use as a port number
sed "s/192.168.20//" /metadata > /metaport
sed -i "s/\.//g" /metaport
If you have another way without using sed im open for those suggestions as well!!
Thanks!

Answer 1

I would prefer using awk for number manipulation rather than sed
awk -F'.' '{printf "%03s%03s\n", $3, $4}' /metadata | cut -c3-6 > /metaport
Input IP:
192.168.202.3
192.168.202.23
192.168.202.254
Output Port:
2003
3023
2254
EDIT
More concise awk only solution avoiding need of cut (Suggested by Jonathan Leffler)
awk -F'.' '{printf "%d%03d\n", $3 % 10, $4}' /metadata > /metaport

Answer 2

If the input file contains only an IP address, then brute force and ignorance can do the job:
sed -e 's/\([0-9]\)\.\([0-9]\)$/& = Port \100\2/' \
-e 's/\([0-9]\)\.\([0-9][0-9]\)$/& = Port \10\2/' \
-e 's/\([0-9]\)\.\([0-9][0-9][0-9]\)$/& = Port \1\2/'
The first expression deals with 1 digit; the second with 2 digits; the third with 3.
Given input data:
192.168.202.3
192.168.203.13
192.168.202.003
192.168.202.254
the output is:
192.168.202.3 = Port 2003
192.168.203.13 = Port 3013
192.168.202.003 = Port 2003
192.168.202.254 = Port 2254
If you have a different input data format, you have to work harder to isolate the relevant section of the IP address, but you should really, really show what the input data looks like.

Answer 3

Just for fun, bash:
while IFS=. read a b c d; do
printf "%d%03d\n" $((c%10)) $d
done <<END
192.168.202.3
192.168.202.003
192.168.209.123
127.0.0.1
END
2003
2003
9123
0001

Answer 4

Given the description -- only insert two zeros when we only have 2 digits into the port the following should work:
sed -r '/Port [0123456789]{2}$/s/Port (.)/\100/'
So this only matches when Port is followed by 2 digits. If it does match, replace the first digit with that digit and two zeros.
If you need to handle 3 digits, another match section that does just 3 digits could be trivially added.