Date and Time Manipulation

Datetime cycling suites inevitably involve performing some form of datetime arithmetic. In the weather forecasting suite we wrote in the Cylc tutorial this arithmetic was done using the cylc cyclepoint command. For example we calculated the cycle point three hours before the present cycle using:

cylc cyclepoint --offset-hours=-3

Rose provides the rose date command which provides functionality beyond cylc cyclepoint as well as the ROSE_DATAC environment variable which provides an easy way to get the path of the share/cycle directory.

The rose date Command

The rose date command provides functionality for:

  • Parsing and formatting datetimes e.g:

    $ rose date '12-31-2000' --parse-format='%m-%d-%Y'
    $ rose date '12-31-2000' --parse-format='%m-%d-%Y' --format='DD-MM-CCYY'
  • Adding offsets to datetimes e.g:

    $ rose date '2000-01-01T0000Z' --offset '+P1M'
  • Calculating the duration between two datetimes e.g:

    $ rose date '2000' '2001'  # Note - 2000 was a leap year!

See the rose date command reference for more information.

Using rose date In A Suite

In datetime cycling suites rose date can work with the cyclepoint using the CYLC_TASK_CYCLE_POINT environment variable:

        script = rose date $CYLC_TASK_CYCLE_POINT --format='MM-DD-CCYY'

Alternatively, if you are providing the standard Rose task environment using rose task-env then rose date can use the -c option to pick up the cycle point:

        env-script = eval $(rose task-env)
        script = rose date -c --format='MM-DD-CCYY'

The ROSE_DATAC Environment Variable

There are two locations where task output is likely to be located:

The work directory

Each task is executed within its work directory which is located in:

<run directory>/work/<cycle>/<task-name>

The path to a task’s work directory can be obtained from the CYLC_TASK_WORK_DIR environment variable.

The share directory

The share directory serves the purpose of providing a storage place for any files which need to be shared between different tasks.

Within the share directory data is typically stored within cycle subdirectories i.e:

<run directory>/share/<cycle>

These are called the share/cycle directories.

The path to the root of the share directory is provided by the CYLC_SUITE_SHARE_DIR environment variable so the path to the cycle subdirectory would be:


The rose task-env command provides the environment variable ROSE_DATAC which is a more convenient way to obtain the path of the share/cycle directory.

To get the path to a previous (or a future) share/cycle directory we can provide an offset to rose task-env e.g:

rose task-env --cycle-offset=PT1H

The path is then made available as the ROSE_DATACPT1H environment variable.