Quotation Marks and \ in Bash Scripting with sed command

Question

Im writing a bash script to help me set up my rpi's network interfaces faster. It is mostly finished now and works using sed to alter different parts of the /etc/network/interfaces files depending how the network interface is being set up. My problem is that i am inserting quotation marks where i don't want them and if i remove the quotation marks i insert the variables containing the data to be inserted as a string of the variable name as oppose to inserting them as their value.

My code is as followed (although i have cut it down)

#!/bin/bash
ANS=''
ssid=''
psk=''
file='/etc/network/interfaces'
ip=''
netmask=''
broadcast=''
gateway=''
function static {
    echo 'Will now set up Static IP'
    echo 'What IP address do you want to assign this Device?'
    echo -e '> \c'
    read ip
    echo 'What is your Networks Netmask/Subnet?'
    echo -e '> \c'
    read netmask
        echo 'What is your Networks Broadcast Address?'
        echo -e '> \c'
        read broadcast
        echo 'What is the address of your Networks Gateway?'
        echo -e '> \c'
        read gateway
    echo 'You entered the following information about your Network'
    echo ''
    echo 'Address: ' $ip
    echo 'Netmask: ' $netmask
    echo 'Broadcast: ' $broadcast
    echo 'Gateway: ' $gateway
    echo 'Is this information correct? (y/n)'
    echo -e '> \c'
        read ANS
        if [ $ANS = 'y' ]; then
        sed -i "s/^iface eth0 inet dhcp.*\$/iface eth0 inet static/" $file
        sed -i "s/^#    address.*\$/    address \"$ip\"/" $file
        sed -i "s/^#    netmask.*\$/    netmask \"$netmask\"/" $file
        sed -i "s/^#    broadcast.*\$/  broadcast \"$broadcast\"/" $file
        sed -i "s/^#    gateway.*\$/    gateway \"$gateway\"/" $file
        echo 'Static IP address has now been set up'
        start
    else
        static
    fi
}

The problem is these lines here

        sed -i "s/^#    address.*\$/    address \"$ip\"/" $file
        sed -i "s/^#    netmask.*\$/    netmask \"$netmask\"/" $file
        sed -i "s/^#    broadcast.*\$/  broadcast \"$broadcast\"/" $file
        sed -i "s/^#    gateway.*\$/    gateway \"$gateway\"/" $file

which insert address "(var_address)". As i said i can get it to insert address $address. But not, as i want, address (var_address). Could someone please explain how to use the / and \ together with " and ' in the sed command so that i can fix the problem. As you may have guessed im a bit of a newb to bash so any help is appreciated.

Answer 1

While bash won't try to resolv no standard variables, like $/, you could simply:

sed "
    /^iface $iface/,/^$/{
        /address/s/^.*$/\taddress $ip/;
        /netmask/s/^.*$/\tnetmask $netmask/;
        /broadcast/s/^.*$/\tbroadcast $broadcast/;
        /gateway/s/^.*$/\tgateway $gateway/;

    }" -i $file

Nota: This modify only 1 paragraph concerning $iface: with the first sed line: /^iface $iface/,/^$/{ ... } delimit a command block who could be executed only from a line matching /^iface $iface/ to an empty line (or end of file).

And for playing with IP address in bash, take a look at https://serverfault.com/a/461831/142978

Answer 2

If I understand what's desired properly, this should work:

sed -i "s/^#    address.*\$/    address $ip/" $file
sed -i "s/^#    netmask.*\$/    netmask $netmask/" $file
sed -i "s/^#    broadcast.*\$/  broadcast $broadcast/" $file
sed -i "s/^#    gateway.*\$/    gateway $gateway/" $file