Repeat using time instants

repeat datetime and repeat datetimelist allow iterating a node over a sequence of date+time instants (formatted as yyyymmddTHHMMSS). They complement repeat date and repeat datelist when sub-daily precision is needed — for example, iterating over hourly or six-hourly data.

Generated variables

Both repeat datetime and repeat datetimelist generate the same set of variables, which can be used in job scripts (%INSTANT%, %INSTANT_DATE%, …) and in trigger/complete expressions:

Variable	Content
`INSTANT`	Current instant, formatted as `YYYYMMDDThhmmss`
`CYCLE_DATE`	Date part, formatted as `YYYYMMDD`
`INSTANT_YYYY`	Four-digit year
`INSTANT_MM`	Two-digit month
`INSTANT_DD`	Two-digit day of month
`INSTANT_DOW`	Day of week
`INSTANT_TIME`	Time part, formatted as `hhmmss`
`INSTANT_HOURS`	Two-digit hour
`INSTANT_MINUTES`	Two-digit minute
`INSTANT_SECONDS`	Two-digit second
`INSTANT_JULIAN`	Julian day corresponding to the date

Choosing between the two

Use repeat datetime when the instants follow a regular interval: a start, an end, and a fixed step (e.g. every 6 hours).
Use repeat datetimelist when the instants are irregular or explicitly enumerated (e.g. 00Z on Monday, 12Z on Wednesday, 06Z on Friday).

Listing 123 Regular interval — repeat datetime

family cycles
  repeat datetime INSTANT 20240101T000000 20240103T180000 06:00:00
  task forecast
  task post
    trigger forecast == complete
endfamily

Listing 124 Irregular instants — repeat datetimelist

family cycles
  repeat datetimelist INSTANT 20240101T000000 20240101T120000 20240103T060000
  task forecast
  task post
    trigger forecast == complete
endfamily

Time instance dependency

A common pattern with repeat datetime and repeat datetimelist is to trigger an overall post-processing task once a specific iteration — identified by its position in the list — has been processed. Because the repeat variable is compared as seconds since epoch, any datetime literal in a trigger expression acts as an index threshold: f:INSTANT >= 20240101T120000 becomes true the moment the repeat advances to the second instant (index 1) or beyond. Combining this with f/post == complete ensures the per-cycle work has actually finished before the overall task starts.

Listing 125 Overall post-processing triggered at specific instants

suite s
  family f
    repeat datetimelist INSTANT 20240101T000000 20240101T120000 20240103T060000
    task forecast
    task post
      trigger forecast == complete
  endfamily
  task overall_1
    # triggered once the index-1 instant (20240101T120000) has completed
    trigger f:INSTANT >= 20240101T120000 and f/post == complete
  task overall_2
    # triggered once the index-2 instant (20240103T060000) has completed
    trigger overall_1 == complete and f:INSTANT >= 20240103T060000 and f/post == complete
endsuite

Chaining overall_2 on overall_1 == complete guarantees the intermediate step always precedes the final one, even if the repeat advances through multiple instants quickly.

Trigger expressions and arithmetic

When a repeat datetime or repeat datetimelist variable is referenced in a trigger expression, its value is the number of seconds since 19700101T000000. Integer arithmetic (adding/subtracting seconds) applies:

# task starts only after t1 has started processing, at least, 20240101T060000
trigger /suite/t1:INSTANT >= 20240101T060000

# task starts only after t1 has started processing at least 1 day past 20240101T060000
trigger /suite/t1:INSTANT + 86400 > 20240101T000000

Tip

DateTime instant literals in trigger expressions (e.g. 20240101T060000) are also interpreted as seconds since epoch, so comparisons between repeat variables and datetime literals work directly without any conversion.

repeat	Full description of all repeat types, generated variables, and trigger semantics
Cron, repeat day 1, repeat date	Analogous patterns using date-based repeats
Python API	`ecflow.RepeatDateTime`, `ecflow.RepeatDateTimeList`