Depending on what else you want to do along with the conversion it might be good to do it in shell. Using the typeset-abilities of the Korn shell:

Code:

typeset -RZ3 b1=""
typeset -RZ3 b2=""
typeset -RZ3 b3=""
typeset -RZ3 b4=""

while IFS='.' read b1 b2 b3 b4 ; do
     print - "$b1.$b2.$b3.$b4"
done <<-EOF
1.2.3.4
12.13.14.15
123.234.1.15
EOF

-R right-justifies the variables content, -Z fills with zeroes (instead of blanks) and 3 fixes the length to 3 digits. i.e "1" becomes "001" therefore. Every value assigned to a variable defined that way will automatically converted to this format.

The loop is just there to showcase how to split the input into 4 variables, do the conversion and put the parts together again without any external tool.

I hope this helps.

bakunin