Cron Expression Parser

The parser takes a single argument which is a well-formed cron expression as is specified BSD's crontab(5)
(excluding any of the special strings @yearly, @monthly, @weekly etc.). The program then outputs a table
where each field of the expression is expanded.

For example the expression */15 0 1,15 * 1-5 /usr/bin/find will produce the following output:

minutes        0 15 30 45
hours          0
day of month   1 15
month          1 2 3 4 5 6 7 8 9 10 11 12
day of week    1 2 3 4 5
command        /usr/bin/find

---

Usage

From project root, run: ./cronparser "{well-formed-cron-expression}" (please note, the expression must be surrounded in quotes).

Example

[user@host cronparser]> ./cronparser "3-59/15 9-17/2 * jan,feb,mar * /usr/bin/find"
minutes        3 18 33 48
hours          9 11 13 15
day of month   1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
month          1 2 3
day of week    0 1 2 3 4 5 6 7
command        /usr/bin/find

Allowed values

Field	Allowed Values	Allowed special characters	Mandatory?
Minutes	0-59	* , - /	Yes
Hours	0-23	* , - /	Yes
Month	1-12 (or 3 character names jan-feb)	* , - /	Yes
Day of month	1-31	* , - /	Yes
Day of week	0-7 (0 & 7 is Sun, or 3 character names mon-sun)	* , - /	Yes
Year	1000-2022	* , - /	No

The order of the fields must be preserved and all fields are manadatory.