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Accepted
Roboman1723
Asked: 2014-12-06 11:05:21 +0800 CST

Bash command to convert IP addresses into their "reverse" form?

  • 772

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

nslookup 192.168.1.123

Current output:

41.31.211.111

Desired output:

111.211.31.41

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

command-line

2 Answers

  1. Best Answer
    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}'
    • 11

  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
}

    set with a string argument tokenizes this string into $1, $2, etc based on the current value of IFS. So we are breaking up the function's input argument $1 into tokens, which now replace the original $1, $2, etc. Because IFS is a dot, the input value in the original $1 gets split up on dots. The dash -- is a safety measure to signal the end of options to set, in case the actual value of $1 would start with a dash (without the -- you would then get an "unknown option" error, or, worse, random or even insecure behavior).

    • 2