How Crontab the best way in scheduling jobs simplified

A crontab file contains entries for each cron job. Entries are separated by newline characters. Each crontab file entry contains six fields separated by spaces or tabs in the following form:

minute  hour  day_of_month  month  weekday  command

Also Read: The best Job Scheduling Interview Questions

These fields accept the following values:

Item Description
minute 0 through 59
hour 0 through 23
day_of_month 1 through 31
month 1 through 12
weekday 0 through 6 for Sunday through Saturday
command a shell command

You must specify a value for each field. Except for the command field, these fields can contain the following:

  • A number in the specified range. To run a command in May, specify 5 in the month field.
  • Two numbers separated by a dash to indicate an inclusive range. To run a cron job on Tuesday through Friday, place 2-5 in the weekday field.
  • A list of numbers separated by commas. To run a command on the first and last day of January, you would specify 1,31 in the day_of_month field.
  • A combination of two numbers separated by a dash to indicate an inclusive range and a list of numbers separated by commas can be used in conjunction. To run a command on the first, tenth to sixteenth and last day of January, you would specify 1,10-16,31 in the day_of_month field. The above two points can also be used in combination.
  • An * (asterisk), meaning all allowed values. To run a job every hour, specify an asterisk in the hour field.

Note: Any character preceded by a backslash (including the %) causes that character to be treated literally. The specification of days may be made by two fields (day of the month and day of the week). If you specify both as a list of elements, both are adhered to. For example, the following entry:

0 0 1,15 * 1 command

would run command on the first and fifteenth days of each month, as well as every Monday. To specify days by only one field, the other field should contain an * .

Specifying Commands

The cron daemon runs the command named in the sixth field at the selected date and time. If you include a % (percent sign) in the sixth field, the cron daemon treats everything that precedes it as the command invocation and makes all that follows it available to standard input, unless you escape the percent sign (\%). Blank lines and lines whose first non-blank character is the number sign (#) will be ignored. If the arguments to the command have a backslash (‘\’), the backslash should be preceded by another backslash.

The best explained Void, Reversal and Returns

The below are the best expalined terms on Void, Return and Reversals in credit cards domain.

What’s the difference between Reversal, Refund/Credit and a Void?
If your customer changes their mind on a product/service that same day and you hadn’t settled or batched your terminal yet, you would want to do a REVERSAL.

If it was after you settled or batched you would do a REFUND.

At the end of the day, you print a detail report and see that there is an error with a transaction, or you decide you don’t want to process that particular transaction; you then would also do a REVERSAL which is the same thing as a VOID to remove that transaction before you settled or batched.

Technically, after the required update to your terminal is completed, REVERSALS and VOIDS will do the same thing. Ref:Here