Passing multiple arguments from input file, to a command multiple times (Bash) - bash

Question

I have found myself in several situations, where it would be handy to be able to feed a command arguments from an input file, on a per line basis. In the handful of times I've wanted to be able to do this, I've ended up finding a workaround or running the command multiple times manually.
I have a file input.txt which contains multiple lines, with an arbitrary number of arguments on each line. I am going to use my most recent need for this functionality as an example. I am trying to simply copy my iptables rules to ip6tables. I have run the command iptables -S > input.txt to generate the following file:
-P INPUT DROP
-P FORWARD DROP
-P OUTPUT DROP
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 80 -m state --state ESTABLISHED -j ACCEPT
-A INPUT -p tcp -m tcp --dport 443 -m state --state ESTABLISHED -j ACCEPT
-A OUTPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A OUTPUT -o lo -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 53 -m state --state NEW -j ACCEPT
-A OUTPUT -p udp -m udp --dport 53 -m state --state NEW -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 80 -m state --state NEW -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 443 -m state --state NEW -j ACCEPT
For each line, I would like to run something like sudo ip6tables $line, so that ip6tables runs with all the arguments from a given line, and N commands are run, where N is the number of lines in input.txt.
The answer to this question should be applicable to this scenario in general. I am not looking for a solution that only works for copying iptables rules to the IPv6 counterpart (through some functionality in iptables for example). I would also prefer a one liner that I can execute in the terminal if possible, instead of writing a bash script. Though, if a bash script turns out to be much less cumbersome than a one liner, then I would accept that as an answer as well.

Answer 1

This sounds like the perfect job for xargs. For your iptables example it works like this:
xargs -L 1 sudo ip6tables < input.txt
xargs reads command arguments from stdin and executes the provided command with the arguments added to the command line. Here the arguments are piped in to stdin from the input.txt file. -L 1 limits the arguments to one line per execution, i.e. one line is added to the command line, the resulting command gets executed, continue with the next line etc.

Answer 2

If it is just for iptables your system may already have an appropriate iptables-restore command you just have to call with:
sudo iptables-restore input.txt
Now if input.txt is to be used to pass arguments to other commands, there i s an easy solution with Bash:
arguments is an array that is read (filled) from each line of input.txt
Iterate over each line of the input.txt file.
Pass the arguments array to your command like this:
#!/usr/bin/env bash
arguments=()
while read -r -a arguments; do
your_command "${arguments[#]}"
done <input.txt
for a one-liner of the above:
while read -ra a;do your_command "${a[#]}";done<input.txt
Or for a POSIX compatible version (no array):
while read -r a;do set -- $a; your_command "$#";done <input.txt