Awk scripts for reading and editing Ubuntu /etc/network/interfaces file (Part 2/2)

For modifying the /etc/network/interfaces file, I use another script and it is slightly more complicated.

[ Modified 28/Nov/14 ] – Created a new github repository for this script

[ Modified 22/May/14 ] – Added feature to remove an interface definition

Edit the interfaces file

Here is the awk script, changeInterface.awk for modifying the interfaces file.

function writeStatic(addr, nw, nm, gw) {
    if (length(addr))
        print "    address ", addr
 
    if (length(nw))
        print "    network ", nw
 
    if (length(nm))
        print "    netmask ", nm
 
    if (length(gw))
        print "    gateway ", gw
}
 
function usage() {
    print "awk -f changeInterfaces.awk <interfaces file> device=<eth device> \n" \
        "       [address=<ip addr>] [gateway=<ip addr>] [netmask=<ip addr>]\n" \
        "       [network=<ip addr>] [mode=dhcp|static] [arg=debug]"
}
 
BEGIN { start = 0;
 
    if (ARGC < 3 || ARGC > 9) {
        usage();
        exit 1;
    }
 
    for (i = 2; i < ARGC; i++) {
        split(ARGV[i], pair, "=");
        if (pair[1] == "address")
            address = pair[2];
        else if (pair[1] == "gateway")
            gateway = pair[2];
        else if (pair[1] == "network")
            network = pair[2];
        else if (pair[1] == "netmask")
            netmask = pair[2];
        else if (pair[1] == "device")
            device = pair[2];
        else if (pair[1] == "arg" && pair[2] == "debug")
            debug = 1;
        else if (pair[1] == "mode" && pair[2] == "dhcp")
            dhcp = 1;
        else if (pair[1] == "mode" && pair[2] == "static")
            static = 1;
        else if (pair[1] == "mode" && pair[2] == "remove")
            remove = 1;
        else {
            usage();
            exit 1;
        }
    }
 
    # Sort out the logic of argument
    if (dhcp && (length(network) || length(gateway) || length(address) || length(netmask))) {
        print "Both DHCP and static properties are defined";
        usage();
        exit 1;
    }
}
 
{
    if ($1 == "auto" && remove) {
        gsub(device, "");
        print;
        next;
    }

    # Look for iface line and if the interface comes with the device name
    # scan whether it is dhcp or static
    if ($1 == "iface")  {
 
        # Ethernet name matches - switch the line scanning on
        if ($2 == device) {
 
            if (debug)
                print $0;
 
            # If remove is defined, switch on delete mode 
            if (remove) {
                definedRemove=1;
            }

            # It's a DHCP interface, if defined any static properties
            # change it to static
            else if (match($0, / dhcp/)) {
                definedDhcp=1;
                # Change to static if defined properties
                if (length(address) || length (gateway) ||
                    length(netmask) || length (network) || static) {
                    print "iface", device, "inet static";
                    next;
                }
            }
 
            # It's a static network interface
            else if (match ($0, / static/)) {
                definedStatic=1;
                # Change to dhcp if defined
                if (dhcp) {
                    sub(/ static/, " dhcp");
                    print $0;
                    next;
                }
            }
 
        }
        # If it is other inteface line, switch it off
        else {
            definedStatic = 0;
            definedDhcp = 0;
            definedRemove = 0;
        }
 
        if (!definedRemove) {
            print $0;
            next;
        }
    }
 
    # Reaches here - means non iface lines
    # Change the static content
    if (definedStatic) {
 
        # Already defined static, just changing the properties
        # Otherwise omit everything until the iface section is
        # finished
        if (!dhcp) {
 
            if (debug)
                print "static - ", $0, $1;
 
            if ($1 == "address" && length(address))
                print "    address ", address
 
            else if ($1 == "netmask" && length(netmask))
                print "    netmask ", netmask;
 
            else if ($1 == "gateway" && length(gateway))
                print "    gateway ", gateway;
 
            else if ($1 == "network" && length(network))
                print "    network ", network;
 
            else
                print $0;
        }
        next;
    }
 
    # If already defined dhcp, then dump the network properties
    if (definedDhcp) {
        writeStatic(address, network, netmask, gateway);
        definedDhcp = 0;
        next;
    }
 
    if (!definedRemove) {
        print $0;
    }
}
 
END {
    # This bit is useful at the condition when the last line is
    # iface dhcp
    if (definedDhcp)
        writeStatic(address, network, netmask, gateway);
}

Suppose we have the following interfaces file setup

auto lo
iface lo inet loopback

auto eth0 eth1 eth2 eth3

iface eth0 inet static
    address 10.0.11.100
    netmask 255.255.255.0
    gateway 10.0.11.1

iface eth1 inet manual
    up ifconfig $IFACE 0.0.0.0 up
    down ifconfig $IFACE down

iface eth2 inet static
    address 192.168.1.2
    netmask 255.255.255.0
    gateway 192.168.1.254

iface eth3 inet dhcp

Script Usage
The script can

1. change a static address properties from an interface defined as static
2. convert an interface with static/manual properties to DHCP and vice versa
3. remove an existing interface definition

Usage 1. Change network static properties

You can define partial or the full set of static properties.

awk -f changeInterface.awk /etc/network/interfaces device=<device> [address=<ip>]  [gateway=<ip>] [netmask=<ip>] [network=<ip>]

Here is a screenshot of an usage example

Usage 2A. Change static/manual interface to DHCP

You can use the script to change static/manual interface to DHCP, simple with mode=dhcp on the target device. The following is a screenshot of the usage

Usage 2B. Change DHCP interface to static address

The script also works for changing a DHCP network interface into a permanent static address setting, simple specify the static properties.

Usage 3. Remove an interface definition

Hopefully, some of you may find this script useful. If you find the script not working probably for your Ubuntu interfaces file, drop me a note with the interface file and I will do my best to fix the script. Thanks.

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