cat crontab.txt

# Crontab Environmental settings
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
00 3 * 7 0 /path/to/command
#15 20 * 1-7 * /path/to/command2
*/30 7,21 1-15 1 * /path/to/another/command
# m h dom mon dow user  command
21 *    * * *   root    cd / && run-parts --report /etc/cron.hourly
0,30 6    * * *   root    test -x /usr/sbin/blah
#47 6    * * 7   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly )
52 6    1 * *   root    test -x /usr/sbin/blahblah || ( cd / && run-parts )


cat crontab.txt | perl cron-explain.pl

Tue Nov 27 14:21:00 2018 => ( 21 * * * * ) => root cd / && run-parts --report /etc/cron.hourly
Wed Nov 28 06:00:00 2018 => ( 0,30 6 * * * ) => root test -x /usr/sbin/blah
Sat Dec  1 06:52:00 2018 => ( 52 6 1 * * ) => root test -x /usr/sbin/blahblah || ( cd / && run-parts )
Tue Jan  1 07:00:00 2019 => ( */30 7,21 1-15 1 * ) => /path/to/another/command
Sun Jul  7 03:00:00 2019 => ( 00 3 * 7 0 ) => /path/to/command


cat crontab.txt | perl cron-explain.pl -n 3

Tue Nov 27 14:21:00 2018 => ( 21 * * * * ) => root cd / && run-parts --report /etc/cron.hourly
Tue Nov 27 15:21:00 2018
Tue Nov 27 16:21:00 2018
Wed Nov 28 06:00:00 2018 => ( 0,30 6 * * * ) => root test -x /usr/sbin/blah
Wed Nov 28 06:30:00 2018
Thu Nov 29 06:00:00 2018
Sat Dec  1 06:52:00 2018 => ( 52 6 1 * * ) => root test -x /usr/sbin/blahblah || ( cd / && run-parts )
Tue Jan  1 06:52:00 2019
Fri Feb  1 06:52:00 2019
Tue Jan  1 07:00:00 2019 => ( */30 7,21 1-15 1 * ) => /path/to/another/command
Tue Jan  1 07:30:00 2019
Tue Jan  1 21:00:00 2019
Sun Jul  7 03:00:00 2019 => ( 00 3 * 7 0 ) => /path/to/command
Sun Jul 14 03:00:00 2019
Sun Jul 21 03:00:00 2019


perl cron-explain.pl -c "2-5 9 12 4 *" -n 4

Fri Apr 12 09:02:00 2019 => ( 2-5 9 12 4 * )
Fri Apr 12 09:03:00 2019
Fri Apr 12 09:04:00 2019
Fri Apr 12 09:05:00 2019