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I'm trying to run a script (zfssnap.sh) to automate snapshots, but one of the arguments needs to change based on which time entry triggers the script to start. With cron, I would just add a new line with the changed argument and set the time fields accordingly.

In reading the launchd and launchd.conf man pages, I'm not seeing any way to associate an argument with a specific StartCalendarInterval key entry. This seems like a significant limitation, so perhaps I'm missing something?

Is there a way change an argument based on the time the script is being run? Or, do I have to make a new plist for each of the situations I'm trying to satisfy?

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The "standard" thing to do is make a new .plist for each different time/argument combo. This is essentially the equivalent of making multiple entries in the crontab, except that each "entry" is an entire file, not just a line.

There's a good example of this in macOS's launch daemon entries for the periodic maintenance program. /System/Library/LaunchDaemons/com.apple.periodic-daily.plist runs /usr/libexec/periodic-wrapper with the argument "daily" and a 24-hour interval, ...periodic-weekly.plist runs it with the argument "weekly" and a 7-day interval, and ...periodic-monthly.plist runs it with the argument "monthly" and a 30.44-day interval.

  • I decided to go this way, but what a PITA. I wish Apple would make this more flexible since they've deprecated cron. In any case, I'm still having trouble getting one of them to work. The argument is <string>pool/dataset</string> and I'm thinking launchd is treating as a path instead of a simple argument being passed to the script. I may still have to run a separate script for that one. – tim.rohrer Sep 8 '18 at 2:12
  • @tim.rohrer It should be treated as a plain string, with no interpretation at all applied (it doesn't even expand ~ or wildcards unless you set the EnableGlobbing key). Can you tell what the script is receiving as its argument? – Gordon Davisson Sep 8 '18 at 2:18
  • zxfer from https://github.com/allanjude/zxfer. The launchd status code is 3, which I've not yet been able to find defined. I can take the same command line and arguments from the plist and it appears to run successfully. Here is a pastebin of the plist: pastebin.com/VAeGeN4E – tim.rohrer Sep 8 '18 at 3:09
  • I'm not familiar with zxfer, but I don't see anything obviously wrong. One thing to check: do all of the .plists have different Label values? – Gordon Davisson Sep 8 '18 at 11:29
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    I'd expect that to be a code from zxfer, but its man page says "exits 0 on success, 1 on an error and 2 if a command line option is incorrect"... so I don't know. Try adding StandardOutPath and StandardErrorPath keys (pointing to reasonable log locations) so you can see if it's printing any helpful errors. Also, check /var/log/system.log for messages from launchd (although I'm not sure it still sends anything useful there). – Gordon Davisson Sep 8 '18 at 18:16

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