#!/bin/bash

# =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~
# IP Address parsing revisited
# =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~ =~
#
# An IP address looks like this:
#       192.168.0.5
# Four groups of 1-3 numbers in the range 0..255 separated by dots.
#
re='^([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})$'

#
# The address is expected as the only argument
#
if [[ $# -ne 1 ]]; then
    echo "Usage: $0 IP_address"
    exit 1
fi

#
# Validate against the regex
#
if [[ $1 =~ $re ]]; then
    #
    # Look at the components and check they are all in range
    #
    errs=0
    problems=
    for i in {1..4}; do
        d="${BASH_REMATCH[$i]}"
        if [[ $d -lt 0 || $d -gt 255 ]]; then
            ((errs++))
            problems+="$d "
        fi
    done

    #
    # Report any problems found
    #
    if [[ $errs -gt 0 ]]; then
        problems="${problems:0:-1}"
        echo "$1 is not a valid IP address; contains ${problems// /, }"
        exit 1
    fi

    echo "$1 is a valid IP address"
else
    echo "$1 is not a valid IP address"
fi