ipgen

#!/bin/sh

help_and_exit() {
    cat << EOF
Usage: $0 NAME [PREFIX]
                                     Naming things is hard, so is IP allocation.

Generate an IP address from name and a prefix.

Example:
    > $0 foo 10.1
    10.1.172.189
    > $0 bar 192.168.1
    192.168.1.55
EOF
    exit 1
}

name="$1"

prefix="$2"
if [ ! -z "$prefix" ]; then
    prefix="${prefix%.}."
fi

dots=$(echo "$prefix" | grep -oF . | wc -l)
segs=$((4 - $dots))

if [ -z "$name" ]; then
    help_and_exit
fi

ip="$prefix"
hash=$(echo -n "$name" | md5sum)

for i in $(seq $segs); do
    byte="${hash:0:2}"
    hash="${hash:2}"
    if [ "$i" != 1 ]; then
        ip="$ip."
    fi
    current=$(printf '%d' 0x$byte)
    ip="$ip$current"
done

echo "$ip"