Bash command to convert IP addresses into their “reverse” form?

Question

When I run nslookup on an IP (These are all examples)

nslookup 192.168.1.123

Current output:

411.311.211.111

Desired output:

111.211.311.411

I have a script that works just seeing if there's a more efficient way or a built-in nslookup command.

Thanks

Answer 1

echo 411.311.211.111 | awk -F. '{print $4"."$3"." $2"."$1}'

Output:

111.211.311.411

or

echo 411.311.211.111 | awk -F. '{OFS="."; print $4,$3,$2,$1}'

Answer 2

Here is a native function. Call it like reverseip 12.34.56.78 to have it print 78.56.34.12. Call it like reversed=$(reverseip 12.34.56.78) to capture the output into a variable.

reverseip () {
    local IFS
    IFS=.
    set -- $1
    echo $4.$3.$2.$1
}

Answer 3

Using sed:

sed -r 's/([0-9]{1,3}).([0-9]{1,3}).([0-9]{1,3}).([0-9]{1,3})/\4.\3.\2.\1/'

Match IP address and print from last to first(reverse)