Why it is poping with error Marshal data too short on localhost?

Question

My application allows to run shell commands on localhost for these I have written the logic in model:

require "open4"
class Command < ApplicationRecord
    after_save :command_run
    def command_run
        ab=[cm].compact.join("")
        pid, stdin, stdout, stderr = Open4::popen4 ab
        stdin.puts "echo 42.out"
        stdin.puts "echo 42.err 1>&2"
        stdin.close
        ignored, status = Process::waitpid2 pid
        @zr= "pid        : #{ pid .inspect}"
        @pr= "stdout     : #{ stdout.read.strip.inspect }"
        @mr ="stderr     : #{ stderr.read.strip.inspect }"
        @nr = "status     : #{ status.inspect }"
        @rr= "exitstatus : #{ status.exitstatus.inspect }"
    end
end

Error I am getting when I try to run it on localhost:

enter code here Argument Error in Commands#index Showing /home/mifi/bash/app/views/commands/index.html.erb where line #12 raised: marshal data too short

And is there anyway so that I can run the shell script on the command line or how can i extract the output on the browser.