Is there a way to validate crontabs with ruby? I've seen some decent php implementations.
Crontabs are pretty common knowledge, so I will spare the details, though I don't need the keywords like reboot to work. basically just numbers with commas and dashes like so
0 4 25,31 12 2012-2020
Read Validating Crontab Entries with PHP regarding this issue. Same applies to ruby, as regex is a limitation.
Well, it's not the prettiest, though I made something that will split it up and parse it out. This isn't going to be touched very often so I'm not worried about speed, though it should handle everything that whenever cannot handle, such as ranges and comma separated dates, as well as reboot.
how it works?
there is a method called cron_wrong which just adds a base error.
I am using 2 columns, interval and interval_type .
interval_type can be cron, @reboot, minute, hour, day, month, year. if it is minute, hour, day, month, or year, I am just passing the interval and interval_type to whenever and doing interval.send interval_type or using @reboot
The tricky part is when the interval_type is cron -- I am validating that it is indeed a valid cron string
def cron_intervals
non_num_at_beg_or_end = /^[^\d]|[^\d]$/
has_non_nums = /[^\d]/
return if interval_type == '@reboot'
if interval_type != 'cron'
has_non_nums.match(interval) { |str| errors.add :interval, "#{str} must be number" }
errors.add :interval, "can't be blank" if interval.length == 0
return
end
cron = interval.split(' ')
if cron.length != 5
cron_wrong
errors.add :interval, 'Wrong number of arguments supplied, (must be 5 -- minute hour day month year)'
return
end
cron.each do |c|
# return if star or only numbers
if c == '*' || !has_non_nums.match(c)
next
end
non_num_at_beg_or_end.match(c) do |str|
cron_wrong
errors.add :interval, "Non-number '#{str}' found"
return
end
c.split(',').each do |spl_dash|
non_num_at_beg_or_end.match(spl_dash) do |str|
cron_wrong
errors.add :interval, "Non-number '#{str}' found"
return
end
range = spl_dash.split('-')
if range.length < 1 || range.length > 2
cron_wrong
errors.add :interval, "ranges must be between two numbers"
return
elsif range.length == 2 and not (range[0].to_i < range[1].to_i)
cron_wrong
errors.add :interval, "range numbers must be lower-higher"
return
end
range.each do |num|
# should be only numbers at this point
has_non_nums.match(num) do |str|
cron_wrong
errors.add :interval, "Non-number '#{str}' found"
return
end
if num.length.blank?
cron_wrong
errors.add :interval, "No number supplied"
end
end
end
end
end
I used Fugit, the library used by Sidekiq-cron
def valid?(cron_expression)
Fugit::Cron.parse(cron_expression).present?
end
Check out this ruby gem to handle your cron queries:
https://github.com/javan/whenever
Here is an associated railscast episode:
http://railscasts.com/episodes/164-cron-in-ruby
Here is an example of the syntax:
every :day, :at => '12:20am' do
command "echo 'Hi! Its 12:20 am.'"
end
