grepcidr-reverse

grepcidr-reverse

grepcidr-reverse is the opposite of grepcidr.

grepcidr can take a list of IP addresses and tell you which of them fall into one (or more) given IP ranges. By contrast, grepcidr-reverse takes a single IP address and a list of ranges and tells you which, if any, range the given address falls into.

Usage

Synopsis

grepcidr-reverse [--tolerant] IP_ADDRESS

• IP ADDRESS is an IPv4 address in the usual human-readable format, e.g. 192.168.0.1

Description

grepcidr-reverse reads a list of CIDR-notation IP ranges, one per line, from STDIN and checks to see if the IP address given by the first argument is within the range of any of them. When a matching range is found, the matching CIDR-notation is printed back to STDOUT and the program exits immediately. That is, it always outputs the first matching range in the input and then exits, ignoring any additional matching ranges.

When a matching range was found, the program exits with code 0. When a match is not found, it exits with code 1. For any other errors, it exits with a code greater than 1.

Options

• --tolerant Silently ignore any rows in the IP range input that are not valid IP ranges. May be useful if piping input from tools such as iproute2 that may contain words like "default" instead of a range.

Examples

The contrived example: find which range an address falls into from a hard-coded list:

grepcidr-reverse 192.168.1.30 <<< "10.0.0.0/16
172.0.0.0/8
192.168.1.0/24
1.1.1.0/24"

Expected output: 192.168.1.0/24

See which iproute2 route is used to reach the destination address 192.168.1.1

ip route | cut -f1 -d' ' | grepcidr-reverse --tolerant 192.168.1.1

Here we use the --tolerant flag to make grepcidr-reverse silently ignore any rows from ip route that don't start with a valid CIDR range, such as "default".

Building

• Make sure you have the Go developer tools installed. See https://go.dev/doc/install.
• In the project directory, run go get to install dependecies.
• Run make to generate the grepcidr-reverse binary.

Build the debian package

• Do the above
• Install dpkg-deb on your system
• Run make debain. grepcidr-reverse.deb is generated in the "debian" directory.