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Full Discussion: Ruby: "Can't convert nil into String" error
Top Forums Programming Ruby: "Can't convert nil into String" error Post 302767857 by Elvirnith on Thursday 7th of February 2013 03:20:10 PM
Old 02-07-2013
Ruby: "Can't convert nil into String" error
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:

Code:
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:

Code:
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:

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

in relation to
Code:
cron  = CrontabParser.new(crontab_data.join("\n"))

but I'm not really sure of how to deal with this.
Last edited by jim mcnamara; 02-07-2013 at 04:53 PM..
 

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LEARN ABOUT REDHAT

crond

CRON(8) 						      System Manager's Manual							   CRON(8)

NAME

       cron - daemon to execute scheduled commands (Vixie Cron)

SYNOPSIS

       cron

DESCRIPTION

       Cron should be started from /etc/rc or /etc/rc.local.  It will return immediately, so you don't need to start it with '&'.

       Cron searches /var/spool/cron for crontab files which are named after accounts in /etc/passwd; crontabs found are loaded into memory.  Cron
       also searches for /etc/crontab and the files in the /etc/cron.d/ directory, which are in a different format (see  crontab(5)).	Cron  then
       wakes up every minute, examining all stored crontabs, checking each command to see if it should be run in the current minute.  When execut-
       ing commands, any output is mailed to the owner of the crontab (or to the user named in the MAILTO environment variable in the crontab,	if
       such exists).

       Additionally,  cron checks each minute to see if its spool directory's modtime (or the modtime on /etc/crontab) has changed, and if it has,
       cron will then examine the modtime on all crontabs and reload those which have changed.	Thus cron need not be restarted whenever a crontab
       file is modified.  Note that the Crontab(1) command updates the modtime of the spool directory whenever it changes a crontab.

SEE ALSO

       crontab(1), crontab(5)

AUTHOR

       Paul Vixie <paul@vix.com>

4th Berkeley Distribution					 20 December 1993							   CRON(8)
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