4 ms·

Sure, I'll pile on here. To do nontrivial scheduling you'd use the entirely-obvious-and-intuitive syntax described at [0]. For example: Mon,Fri *-01/2-01,03

Sure, I'll pile on here. To do nontrivial scheduling you'd use the entirely-obvious-and-intuitive syntax described at [0]. For example: Mon,Fri *-01/2-01,03 *:30:45 Who'd ever want to go back crontab format for nontrivial scheduling? [1] [0] <https://www.freedesktop.org/software/systemd/man/latest/systemd.time.html#Calendar%20Events https://www.freedesktop.org/software/systemd/man/latest/syst...> [1] This question is sarcasm. SystemD is often like this... dead simple things look dead simple, but complex things are -if they're possible at all- at least as complex as they are everywhere else.

p0358 4mo ago
If you know the syntax, it's still actually rather trivial. Still easier to read than advanced cron magic.
- simoncion 4mo ago
  > Still easier to read than advanced cron magic. Looking at the other examples on that page, I'm gonna say that it's only arguably easier to read for basic stuff... especially if you're familiar with the syntax. The complex stuff is -at best- just as difficult.
harshreality 4mo ago
I found the systemd time spec syntax you referenced to be logical and well thought out. Cron syntax is simpler for the easy cases because cron tries to do less. It ignores years and seconds entirely, and doesn't try to adhere roughly to ISO8601 ordering and field separators, instead using space universally for field separation and euro-style least-to-most significant field ordering. I like ISO8601, so I get along with systemd's style better, despite it introducing slightly more cognitive load. The only thing that threw me for a loop and seems like "special magic" was > "Mon *-05~07/1" means "the last Monday in May." But good luck doing that in one line in cron. Some cron-style libraries seem to support L/W/# for last / nearest-weekday / nth of month, but I don't know if any system crons do. (cronie? dcron? I don't think so. fcron? bcron? I don't see it there either.) '#' is syntactic sugar for DOW + 7-day range, while L is covered by the above quoted syntax. If your cron has that kind of syntax, then for a case like "weekday closest to 1st of month", "W" is more convenient than writing 3 systemd timer rules to cover the three cases (weekday day 1, monday day 2, friday last day of month), but that's a big if. Generally you'd have to write 3 rules in cron anyway.
- Tepix 4mo ago
  > But good luck doing that in one line in cron. Two options: 0 0 25-31 5 1 or, if your cron supports „L“: 0 0 L 5 1
  - harshreality 4mo ago
    The first one works in that specific case, but not more generically. For example, "Last Monday in February", or "last Monday of the month" for multiple months unless they're all 30 or all 31 days.
    - simoncion 4mo ago
      This was fun to cook up and may (or may not!) break if one's locale changes: # Run a command on the last day of the month. Only starts checking at midnight towards the end of the month. Assumes GNU date, which is fair if we're discussing a Linux-only cron-alike. 0 0 28-31 * * if [ $(date +\%d) -eq $(date --date="$(date +\%m)/1 + 1 month - 1 day" +\%d) ]; then /usr/local/bin/runCommand.sh; fi I bet one could do something similar to determine if we're at the "last $NAMED_WEEKDAY in the month" by counting ahead a week and seeing if the month name changes. If I were doing this for real, I'd either switch to a more capable cron, or take a serious try at the date math and then wrap it up as a standalone helper. Or I guess I'd look to see if someone already built that helper. ...I guess...
      - harshreality 4mo ago
        I am curious whether there's a more capable system cron that supports that kind of thing. Quartz job scheduler (java), AWS, and CF obviously wouldn't qualify. I think this is only possible if you're using a heavyweight job scheduler like those. Or... systemd. It ultimately doesn't matter "for real", because almost nobody without some horrific legacy system to integrate with would need to use anything more than lists, ranges, and increments. There's a reason nobody's added these features to system crons. Clever trigger times for events that don't really need to be triggered at clever times... sure, but lacking that capability wouldn't change anything, the trigger would just be a more boring one. Events like "last Friday of the month" or "nearest weekday to the 1st of the month" or even "Friday the 13th" are more for business logic, not system crontabs.
ffaccount2 4mo ago
To be honest it looks rather easy to digest? I can sort of guess the meaning without documentation. For cron, despite years of looking at it, I can never remember what those numbers mean and I need to Google almost every time.

p0358 4mo ago

If you know the syntax, it's still actually rather trivial. Still easier to read than advanced cron magic.

simoncion 4mo ago
> Still easier to read than advanced cron magic. Looking at the other examples on that page, I'm gonna say that it's only arguably easier to read for basic stuff... especially if you're familiar with the syntax. The complex stuff is -at best- just as difficult.

harshreality 4mo ago

I found the systemd time spec syntax you referenced to be logical and well thought out. Cron syntax is simpler for the easy cases because cron tries to do less. It ignores years and seconds entirely, and doesn't try to adhere roughly to ISO8601 ordering and field separators, instead using space universally for field separation and euro-style least-to-most significant field ordering. I like ISO8601, so I get along with systemd's style better, despite it introducing slightly more cognitive load. The only thing that threw me for a loop and seems like "special magic" was > "Mon *-05~07/1" means "the last Monday in May." But good luck doing that in one line in cron. Some cron-style libraries seem to support L/W/# for last / nearest-weekday / nth of month, but I don't know if any system crons do. (cronie? dcron? I don't think so. fcron? bcron? I don't see it there either.) '#' is syntactic sugar for DOW + 7-day range, while L is covered by the above quoted syntax. If your cron has that kind of syntax, then for a case like "weekday closest to 1st of month", "W" is more convenient than writing 3 systemd timer rules to cover the three cases (weekday day 1, monday day 2, friday last day of month), but that's a big if. Generally you'd have to write 3 rules in cron anyway.

Tepix 4mo ago
> But good luck doing that in one line in cron. Two options: 0 0 25-31 5 1 or, if your cron supports „L“: 0 0 L 5 1
- harshreality 4mo ago
  The first one works in that specific case, but not more generically. For example, "Last Monday in February", or "last Monday of the month" for multiple months unless they're all 30 or all 31 days.
  - simoncion 4mo ago
    This was fun to cook up and may (or may not!) break if one's locale changes: # Run a command on the last day of the month. Only starts checking at midnight towards the end of the month. Assumes GNU date, which is fair if we're discussing a Linux-only cron-alike. 0 0 28-31 * * if [ $(date +\%d) -eq $(date --date="$(date +\%m)/1 + 1 month - 1 day" +\%d) ]; then /usr/local/bin/runCommand.sh; fi I bet one could do something similar to determine if we're at the "last $NAMED_WEEKDAY in the month" by counting ahead a week and seeing if the month name changes. If I were doing this for real, I'd either switch to a more capable cron, or take a serious try at the date math and then wrap it up as a standalone helper. Or I guess I'd look to see if someone already built that helper. ...I guess...
    - harshreality 4mo ago
      I am curious whether there's a more capable system cron that supports that kind of thing. Quartz job scheduler (java), AWS, and CF obviously wouldn't qualify. I think this is only possible if you're using a heavyweight job scheduler like those. Or... systemd. It ultimately doesn't matter "for real", because almost nobody without some horrific legacy system to integrate with would need to use anything more than lists, ranges, and increments. There's a reason nobody's added these features to system crons. Clever trigger times for events that don't really need to be triggered at clever times... sure, but lacking that capability wouldn't change anything, the trigger would just be a more boring one. Events like "last Friday of the month" or "nearest weekday to the 1st of the month" or even "Friday the 13th" are more for business logic, not system crontabs.

ffaccount2 4mo ago

To be honest it looks rather easy to digest? I can sort of guess the meaning without documentation. For cron, despite years of looking at it, I can never remember what those numbers mean and I need to Google almost every time.