Ruby: "Can't convert nil into String" error

Applications Programming
1

Hi there,

I'm relatively new to ruby and I'm trying to put together this script to process cron jobs on a server. It's almost working, except I can't figure out what exactly is wrong and how to fix it. Can anyone point me in the right direction?

Here's what I have so far:

require 'rubygems'
require 'crontab-parser'

start_time = Time.parse(ARGV[0])
end_time = Time.parse(ARGV[1])

File.open('/root/flagged_cron_jobs.log', 'w+') do |f2|

crontab_data = File.readlines(ARGV[2]).select {|line| line =~ /^[0-9*]/}
cron  = CrontabParser.new(crontab_data.join("\n"))
(start_time..end_time).each do |timestamp|
  next unless timestamp.sec.to_i == 0
  cron.each do |cron_entry|
Dir["/var/spool/cron/*"].each do |file|
  username = file.split("/").last
  crontab = CrontabParser.new(File.read(file))
  puts "User: #{username}"
    if cron_entry.should_run?(timestamp)
      f2.puts "#{timestamp}\t#{cron_entry.cmd}"

        end
      end
    end
  end
end

Here's the error:

cron_parse.rb:9:in `readlines': can't convert nil into String (TypeError)
	from cron_parse.rb:9
	from cron_parse.rb:7:in `open'
	from cron_parse.rb:7

Command being executed is like so:

ruby cron_parse.rb "Thurs Feb 7 01:00 UTC 2013" "Thurs Feb 7 01:14 UTC 2013"

I suspect it's because of the addition of

 crontab = CrontabParser.new(File.read(file))

in relation to

cron  = CrontabParser.new(crontab_data.join("\n"))

but I'm not really sure of how to deal with this.

2

That is happening because you are running the script wrong. Your script expects 3 arguments as input -- ARGV[0], ARGV[1] and ARGV[2] but you are only providing ARGV[0] and ARGV[1].
Therefore on line 9 ARGV[2] is nil and cannot be converted to a string hence the error. You need to run it like so:

ruby cron_parse.rb "Thurs Feb 7 01:00 UTC 2013" "Thurs Feb 7 01:14 UTC 2013" Filename